<PAGE>   1
                                                  ----------------------------
                                                          OMB APPROVAL
                                                  ----------------------------
                                                  OMB Number:        3235-0145
                                                  Expires:    October 31, 1994
                                                  ----------------------------
                                                  Estimated average burden
                                                  hours per form . . . . 14.90

                                 UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549


                                  SCHEDULE 13D

                   UNDER THE SECURITIES EXCHANGE ACT OF 1934
                          (AMENDMENT NO.     1     )*
                                        -----------

                            20th Century Industries
-------------------------------------------------------------------------------
                                (Name of Issuer)

                        Common Stock, Without Par Value
-------------------------------------------------------------------------------
                         (Title of Class of Securities)

                                  901272 20 3
             ------------------------------------------------------
                                 (CUSIP Number)

                       Richard J. D'Alessandri, Counsel
                       American International Group, Inc.
               70 Pine Street, NYC, NY  10270      (212) 770-5856
-------------------------------------------------------------------------------
          (Name, Address and Telephone Number of Person Authorized to
                      Receive Notices and Communications)

                                 March 23, 1995
             ------------------------------------------------------
             (Date of Event which Requires Filing of this Statement)


If the filing person has previously filed a statement on Schedule 13G to report
the acquisition which is the subject of this Schedule 13D, and is filing this
schedule because of Rule 13d-1(b)(3) or (4), check the following box / /.

Check the following box if a fee is being paid with the statement / /. (A fee is
not required only if the reporting person: (1) has a previous statement on file
reporting beneficial ownership of more than five percent of the class of
securities described in Item 1; and (2) has filed no amendment subsequent
thereto reporting beneficial ownership of five percent or less of such class.)
(See Rule 13d-7.)

NOTE: Six copies of this statement, including all exhibits, should be filed with
the Commission. See  Rule 13d-1(a) for other parties to whom copies are to be
sent.

*The remainder of this cover page shall be filled out for a reporting person's
initial filing on this form with respect to the subject class of securities, and
for any subsequent amendment containing information which would alter
disclosures provided in a prior cover page.

The information required on the remainder of this cover page shall not be deemed
to be "filed" for the purpose of Section 18 of the Securities Exchange Act of
1934 ("Act") or otherwise subject to the liabilities of that section of the Act
but shall be subject to all other provisions of the Act (however, see the
Notes).



<PAGE>   2
                                  SCHEDULE 13D

CUSIP NO.  901272 20 3                                 PAGE       OF      PAGES
          ------------                                      -----    ----

1   NAME OF REPORTING PERSON
    S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON

    American International Group, Inc.
    IRS No. 13-2592361
-------------------------------------------------------------------------------
2   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*                   (a) / /
                                                                        (b) / /

-------------------------------------------------------------------------------
3   SEC USE ONLY


-------------------------------------------------------------------------------
4   SOURCE OF FUNDS*

    WC
-------------------------------------------------------------------------------
5   CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO
    ITEMS 2(d) or 2(e)                                                      / /

-------------------------------------------------------------------------------
6   CITIZENSHIP OR PLACE OF ORGANIZATION

    Incorporated in the State of Delaware
-------------------------------------------------------------------------------
                   7   SOLE VOTING POWER

                   ------------------------------------------------------------
   NUMBER OF       8   SHARED VOTING POWER
     SHARES
  BENEFICIALLY         36,317,475
    OWNED BY       ------------------------------------------------------------
      EACH         9   SOLE DISPOSITIVE POWER
   REPORTING
     PERSON        ------------------------------------------------------------
      WITH         10  SHARED DISPOSITIVE POWER

                       36,317,475
-------------------------------------------------------------------------------
11  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

                       36,317,475
-------------------------------------------------------------------------------
12  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES*  / /

-------------------------------------------------------------------------------
13  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

                       41.80%
-------------------------------------------------------------------------------
14  TYPE OF REPORTING PERSON*

    HC, CO
-------------------------------------------------------------------------------

                     *SEE INSTRUCTIONS BEFORE FILLING OUT!
          INCLUDE BOTH SIDES OF THE COVER PAGE, RESPONSES TO ITEMS 1-7
      (INCLUDING EXHIBITS) OF THE SCHEDULE, AND THE SIGNATURE ATTESTATION.

                                                                         2 OF 7


<PAGE>   3
                                                  ----------------------------
                                                          OMB APPROVAL
                                                  ----------------------------
                                                  OMB Number:        3235-0145
                                                  Expires:    October 31, 1994
                                                  Estimated average burden
                                                  hours per form . . . . 14.90

                                 UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549


                                  SCHEDULE 13D

                   UNDER THE SECURITIES EXCHANGE ACT OF 1934
                          (AMENDMENT NO.     1     )*
                                        -----------

                            20th Century Industries
-------------------------------------------------------------------------------
                                (Name of Issuer)

                        Common Stock, Without Par Value
-------------------------------------------------------------------------------
                         (Title of Class of Securities)

                                  901272 20 3
             ------------------------------------------------------
                                 (CUSIP Number)

                       Richard J. D'Alessandri, Counsel
                       American International Group, Inc.
               70 Pine Street, NYC, NY  10270      (212) 770-5856
-------------------------------------------------------------------------------
          (Name, Address and Telephone Number of Person Authorized to
                      Receive Notices and Communications)

                                 March 23, 1995
             ------------------------------------------------------
             (Date of Event which Requires Filing of this Statement)


If the filing person has previously filed a statement on Schedule 13G to report
the acquisition which is the subject of this Schedule 13D, and is filing this
schedule because of Rule 13d-1(b)(3) or (4), check the following box / /.

Check the following box if a fee is being paid with the statement / /. (A fee is
not required only if the reporting person: (1) has a previous statement on file
reporting beneficial ownership of more than five percent of the class of
securities described in Item 1; and (2) has filed no amendment subsequent
thereto reporting beneficial ownership of five percent or less of such class.)
(See Rule 13d-7.)

NOTE: Six copies of this statement, including all exhibits, should be filed with
the Commission. See  Rule 13d-1(a) for other parties to whom copies are to be
sent.

*The remainder of this cover page shall be filled out for a reporting person's
initial filing on this form with respect to the subject class of securities, and
for any subsequent amendment containing information which would alter
disclosures provided in a prior cover page.

The information required on the remainder of this cover page shall not be deemed
to be "filed" for the purpose of Section 18 of the Securities Exchange Act of
1934 ("Act") or otherwise subject to the liabilities of that section of the Act
but shall be subject to all other provisions of the Act (however, see the
Notes).



<PAGE>   4
                                  SCHEDULE 13D

CUSIP NO.  901272 20 3                                 PAGE       OF      PAGES
          ------------                                      -----    ----

1   NAME OF REPORTING PERSON
    S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON

    American Home Assurance Company
    IRS No. 13-5124990
-------------------------------------------------------------------------------
2   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*                   (a) / /
                                                                        (b) / /

-------------------------------------------------------------------------------
3   SEC USE ONLY


-------------------------------------------------------------------------------
4   SOURCE OF FUNDS*

    WC
-------------------------------------------------------------------------------
5   CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO
    ITEMS 2(d) or 2(e)                                                      / /

-------------------------------------------------------------------------------
6   CITIZENSHIP OR PLACE OF ORGANIZATION

    Incorporated in the State of New York
-------------------------------------------------------------------------------
                   7   SOLE VOTING POWER
                       9,124,125
                   ------------------------------------------------------------
   NUMBER OF       8   SHARED VOTING POWER
     SHARES
  BENEFICIALLY        
    OWNED BY       ------------------------------------------------------------
      EACH         9   SOLE DISPOSITIVE POWER
   REPORTING           9,124,125
     PERSON        ------------------------------------------------------------
      WITH         10  SHARED DISPOSITIVE POWER

                       
-------------------------------------------------------------------------------
11  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

                       9,124,125
-------------------------------------------------------------------------------
12  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES*  / /

-------------------------------------------------------------------------------
13  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

                       10.50%
-------------------------------------------------------------------------------
14  TYPE OF REPORTING PERSON*

    IC, CO
-------------------------------------------------------------------------------

                     *SEE INSTRUCTIONS BEFORE FILLING OUT!
          INCLUDE BOTH SIDES OF THE COVER PAGE, RESPONSES TO ITEMS 1-7
      (INCLUDING EXHIBITS) OF THE SCHEDULE, AND THE SIGNATURE ATTESTATION.

                                                                         2 OF 7


<PAGE>   5
                                                  ----------------------------
                                                          OMB APPROVAL
                                                  ----------------------------
                                                  OMB Number:        3235-0145
                                                  Expires:    October 31, 1994
                                                  Estimated average burden
                                                  hours per form . . . . 14.90

                                 UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549


                                  SCHEDULE 13D

                   UNDER THE SECURITIES EXCHANGE ACT OF 1934
                          (AMENDMENT NO.     1     )*
                                        -----------

                            20th Century Industries
-------------------------------------------------------------------------------
                                (Name of Issuer)

                        Common Stock, Without Par Value
-------------------------------------------------------------------------------
                         (Title of Class of Securities)

                                  901272 20 3
             ------------------------------------------------------
                                 (CUSIP Number)

                       Richard J. D'Alessandri, Counsel
                       American International Group, Inc.
               70 Pine Street, NYC, NY  10270      (212) 770-5856
-------------------------------------------------------------------------------
          (Name, Address and Telephone Number of Person Authorized to
                      Receive Notices and Communications)

                                 March 23, 1995
             ------------------------------------------------------
             (Date of Event which Requires Filing of this Statement)


If the filing person has previously filed a statement on Schedule 13G to report
the acquisition which is the subject of this Schedule 13D, and is filing this
schedule because of Rule 13d-1(b)(3) or (4), check the following box / /.

Check the following box if a fee is being paid with the statement / /. (A fee is
not required only if the reporting person: (1) has a previous statement on file
reporting beneficial ownership of more than five percent of the class of
securities described in Item 1; and (2) has filed no amendment subsequent
thereto reporting beneficial ownership of five percent or less of such class.)
(See Rule 13d-7.)

NOTE: Six copies of this statement, including all exhibits, should be filed with
the Commission. See  Rule 13d-1(a) for other parties to whom copies are to be
sent.

*The remainder of this cover page shall be filled out for a reporting person's
initial filing on this form with respect to the subject class of securities, and
for any subsequent amendment containing information which would alter
disclosures provided in a prior cover page.

The information required on the remainder of this cover page shall not be deemed
to be "filed" for the purpose of Section 18 of the Securities Exchange Act of
1934 ("Act") or otherwise subject to the liabilities of that section of the Act
but shall be subject to all other provisions of the Act (however, see the
Notes).



<PAGE>   6
                                  SCHEDULE 13D

CUSIP NO.  901272 20 3                                 PAGE       OF      PAGES
           ------------                                      -----    ----

1   NAME OF REPORTING PERSON
    S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON

    Commerce & Industry Insurance Company
    IRS No. 31-1938623
-------------------------------------------------------------------------------
2   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*                   (a) / /
                                                                        (b) / /

-------------------------------------------------------------------------------
3   SEC USE ONLY


-------------------------------------------------------------------------------
4   SOURCE OF FUNDS*

    WC
-------------------------------------------------------------------------------
5   CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO
    ITEMS 2(d) or 2(e)                                                      / /

-------------------------------------------------------------------------------
6   CITIZENSHIP OR PLACE OF ORGANIZATION

    Incorporated in the State of New York
-------------------------------------------------------------------------------
                   7   SOLE VOTING POWER
                       5,295,675
                   ------------------------------------------------------------
   NUMBER OF       8   SHARED VOTING POWER
     SHARES
  BENEFICIALLY         
    OWNED BY       ------------------------------------------------------------
      EACH         9   SOLE DISPOSITIVE POWER
   REPORTING           5,295,675
     PERSON        ------------------------------------------------------------
      WITH         10  SHARED DISPOSITIVE POWER

                       
-------------------------------------------------------------------------------
11  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

                       5,295,675
-------------------------------------------------------------------------------
12  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES*  / /

-------------------------------------------------------------------------------
13  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

                       6.09%
-------------------------------------------------------------------------------
14  TYPE OF REPORTING PERSON*

    IC, CO
-------------------------------------------------------------------------------

                     *SEE INSTRUCTIONS BEFORE FILLING OUT!
          INCLUDE BOTH SIDES OF THE COVER PAGE, RESPONSES TO ITEMS 1-7
      (INCLUDING EXHIBITS) OF THE SCHEDULE, AND THE SIGNATURE ATTESTATION.

                                                                         2 OF 7


<PAGE>   7
                                                  ----------------------------
                                                          OMB APPROVAL
                                                  ----------------------------
                                                  OMB Number:        3235-0145
                                                  Expires:    October 31, 1994
                                                  Estimated average burden
                                                  hours per form . . . . 14.90

                                 UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549


                                  SCHEDULE 13D

                   UNDER THE SECURITIES EXCHANGE ACT OF 1934
                          (AMENDMENT NO.     1     )*
                                        -----------

                            20th Century Industries
-------------------------------------------------------------------------------
                                (Name of Issuer)

                        Common Stock, Without Par Value
-------------------------------------------------------------------------------
                         (Title of Class of Securities)

                                  901272 20 3
             ------------------------------------------------------
                                 (CUSIP Number)

                       Richard J. D'Alessandri, Counsel
                       American International Group, Inc.
               70 Pine Street, NYC, NY  10270      (212) 770-5856
-------------------------------------------------------------------------------
          (Name, Address and Telephone Number of Person Authorized to
                      Receive Notices and Communications)

                                 March 23, 1995
             ------------------------------------------------------
             (Date of Event which Requires Filing of this Statement)


If the filing person has previously filed a statement on Schedule 13G to report
the acquisition which is the subject of this Schedule 13D, and is filing this
schedule because of Rule 13d-1(b)(3) or (4), check the following box / /.

Check the following box if a fee is being paid with the statement / /. (A fee is
not required only if the reporting person: (1) has a previous statement on file
reporting beneficial ownership of more than five percent of the class of
securities described in Item 1; and (2) has filed no amendment subsequent
thereto reporting beneficial ownership of five percent or less of such class.)
(See Rule 13d-7.)

NOTE: Six copies of this statement, including all exhibits, should be filed with
the Commission. See  Rule 13d-1(a) for other parties to whom copies are to be
sent.

*The remainder of this cover page shall be filled out for a reporting person's
initial filing on this form with respect to the subject class of securities, and
for any subsequent amendment containing information which would alter
disclosures provided in a prior cover page.

The information required on the remainder of this cover page shall not be deemed
to be "filed" for the purpose of Section 18 of the Securities Exchange Act of
1934 ("Act") or otherwise subject to the liabilities of that section of the Act
but shall be subject to all other provisions of the Act (however, see the
Notes).



<PAGE>   8
                                  SCHEDULE 13D

CUSIP NO.  901272 20 3                                 PAGE       OF      PAGES
           ------------                                     -----    ----

1   NAME OF REPORTING PERSON
    S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON

    New Hampshire Insurance Company    
    IRS No. 02-0172170
-------------------------------------------------------------------------------
2   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*                   (a) / /
                                                                        (b) / /

-------------------------------------------------------------------------------
3   SEC USE ONLY


-------------------------------------------------------------------------------
4   SOURCE OF FUNDS*

    WC
-------------------------------------------------------------------------------
5   CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO
    ITEMS 2(d) or 2(e)                                                      / /

-------------------------------------------------------------------------------
6   CITIZENSHIP OR PLACE OF ORGANIZATION

    Incorporated in the State of Pennsylvania
-------------------------------------------------------------------------------
                   7   SOLE VOTING POWER
                       5,295,675
                   ------------------------------------------------------------
   NUMBER OF       8   SHARED VOTING POWER
     SHARES
  BENEFICIALLY        
    OWNED BY       ------------------------------------------------------------
      EACH         9   SOLE DISPOSITIVE POWER
   REPORTING           5,295,675
     PERSON        ------------------------------------------------------------
      WITH         10  SHARED DISPOSITIVE POWER

                      
-------------------------------------------------------------------------------
11  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

                       5,295,675
-------------------------------------------------------------------------------
12  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES*  / /

-------------------------------------------------------------------------------
13  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

                       6.09%
-------------------------------------------------------------------------------
14  TYPE OF REPORTING PERSON*

    IC, CO
-------------------------------------------------------------------------------

                     *SEE INSTRUCTIONS BEFORE FILLING OUT!
          INCLUDE BOTH SIDES OF THE COVER PAGE, RESPONSES TO ITEMS 1-7
      (INCLUDING EXHIBITS) OF THE SCHEDULE, AND THE SIGNATURE ATTESTATION.

                                                                         2 OF 7


<PAGE>   9
                                                  ----------------------------
                                                          OMB APPROVAL
                                                  ----------------------------
                                                  OMB Number:        3235-0145
                                                  Expires:    October 31, 1994
                                                  Estimated average burden
                                                  hours per form . . . . 14.90

                                 UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549


                                  SCHEDULE 13D

                   UNDER THE SECURITIES EXCHANGE ACT OF 1934
                          (AMENDMENT NO.     1     )*
                                        -----------

                            20th Century Industries
-------------------------------------------------------------------------------
                                (Name of Issuer)

                        Common Stock, Without Par Value
-------------------------------------------------------------------------------
                         (Title of Class of Securities)

                                  901272 20 3
             ------------------------------------------------------
                                 (CUSIP Number)

                       Richard J. D'Alessandri, Counsel
                       American International Group, Inc.
               70 Pine Street, NYC, NY  10270      (212) 770-5856
-------------------------------------------------------------------------------
          (Name, Address and Telephone Number of Person Authorized to
                      Receive Notices and Communications)

                                 March 23, 1995
             ------------------------------------------------------
             (Date of Event which Requires Filing of this Statement)


If the filing person has previously filed a statement on Schedule 13G to report
the acquisition which is the subject of this Schedule 13D, and is filing this
schedule because of Rule 13d-1(b)(3) or (4), check the following box / /.

Check the following box if a fee is being paid with the statement / /. (A fee is
not required only if the reporting person: (1) has a previous statement on file
reporting beneficial ownership of more than five percent of the class of
securities described in Item 1; and (2) has filed no amendment subsequent
thereto reporting beneficial ownership of five percent or less of such class.)
(See Rule 13d-7.)

NOTE: Six copies of this statement, including all exhibits, should be filed with
the Commission. See  Rule 13d-1(a) for other parties to whom copies are to be
sent.

*The remainder of this cover page shall be filled out for a reporting person's
initial filing on this form with respect to the subject class of securities, and
for any subsequent amendment containing information which would alter
disclosures provided in a prior cover page.

The information required on the remainder of this cover page shall not be deemed
to be "filed" for the purpose of Section 18 of the Securities Exchange Act of
1934 ("Act") or otherwise subject to the liabilities of that section of the Act
but shall be subject to all other provisions of the Act (however, see the
Notes).



<PAGE>   10
                                  SCHEDULE 13D

CUSIP NO.  901272 20 3                                 PAGE       OF      PAGES
          ------------                                      -----    ----

1   NAME OF REPORTING PERSON
    S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON

    National Union Fire Insurance Company of Pittsburgh, Pa.
    IRS No. 25-0687550
-------------------------------------------------------------------------------
2   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*                   (a) / /
                                                                        (b) / /

-------------------------------------------------------------------------------
3   SEC USE ONLY


-------------------------------------------------------------------------------
4   SOURCE OF FUNDS*

    WC
-------------------------------------------------------------------------------
5   CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO
    ITEMS 2(d) or 2(e)                                                      / /

-------------------------------------------------------------------------------
6   CITIZENSHIP OR PLACE OF ORGANIZATION

    Incorporated in the State of Pennsylvania
-------------------------------------------------------------------------------
                   7   SOLE VOTING POWER
                       602,000
                   ------------------------------------------------------------
   NUMBER OF       8   SHARED VOTING POWER
     SHARES
  BENEFICIALLY        
    OWNED BY       ------------------------------------------------------------
      EACH         9   SOLE DISPOSITIVE POWER
   REPORTING           602,000
     PERSON        ------------------------------------------------------------
      WITH         10  SHARED DISPOSITIVE POWER

                       
-------------------------------------------------------------------------------
11  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

                       602,000
-------------------------------------------------------------------------------
12  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES*  / /

-------------------------------------------------------------------------------
13  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

                       0.69%
-------------------------------------------------------------------------------
14  TYPE OF REPORTING PERSON*

    IC, CO
-------------------------------------------------------------------------------

                     *SEE INSTRUCTIONS BEFORE FILLING OUT!
          INCLUDE BOTH SIDES OF THE COVER PAGE, RESPONSES TO ITEMS 1-7
      (INCLUDING EXHIBITS) OF THE SCHEDULE, AND THE SIGNATURE ATTESTATION.

                                                                         2 OF 7


<PAGE>   11
ITEM 1.  SECURITY AND ISSUER.

         This statement amends the statement on Schedule 13D dated December 16,
1995 ("Schedule 13D") previously filed by American International Group, Inc., a
Delaware corporation ("AIG") relating to the common stock, without par value
("Common Stock"), of 20th Century Industries, a California corporation
("Company"). The principal executive offices of the Company are located at 6301
Owensmouth Avenue, Woodland Hills, California 91367.

         Each capitalized term used in this statement which is defined in the
Schedule 13D shall have the meaning in the Schedule 13D.

ITEM 2.  IDENTITY AND BACKGROUND.

         (a) through (c). This statement is filed by American International
Group, Inc., a Delaware corporation ("AIG"), on behalf of itself and the AIG
Subs.

         On February 13, 1995, the Company announced that gross losses and
allocated loss adjustment expenses of the Company associated with the Northridge
Quake were then estimated to be $940 million. As a result thereof, AIG and the
Company, on March 23, 1995, consummated the transactions contemplated under
Amendment No. 1 to the Investment and Strategic Alliance Agreement dated on
March 23, 1995 ("Amendment") between the Company and AIG, at which time, for an
aggregate purchase price of $20 million, the Company issued and sold, and
Commerce & Industry purchased, 20,000 additional shares ("Additional Shares") of
the Company's Series A Convertible Preferred Stock.

         A conformed copy of the Amendment setting forth the terms under which
the Additional Shares were issued to Commerce & Industry is attached hereto as
Exhibit A. The descriptions set forth in this Amendment No. 1 to Form 13D are
qualified in their entirety by reference to the Amendment which is attached
hereto.

         AIG is a holding company which, through its subsidiaries, is primarily
engaged in a broad range of insurance and insurance-related activities in the
United States and abroad. AIG, through its subsidiaries, also conducts financial
services activities and agency and fee operations. Each of the AIG Subs is a
multiple line, insurance company which writes substantially all lines of
property and casualty insurance in each state of the United States and abroad.
The principal executive offices of AIG, Commerce & Industry and each of the
other AIG Subs are located at 70 Pine Street, New York, New York 10270.

         (d) through (e). During the last five years, none of AIG, SICO, The
Starr Foundation, Starr, American Home, Commerce & Industry, National Union and
New Hampshire, or any of the Covered

                              PAGE 6 OF ____ PAGES



<PAGE>   12



Persons, has (i) been convicted in a criminal proceeding (excluding traffic
violations or similar misdemeanors) or (ii) been a party to a civil proceeding
of a judicial or administrative body of competent jurisdiction and as a result
of such proceeding was or is subject to a judgment, decree or final order
enjoining future violations of, or prohibiting or mandating activities subject
to federal or state securities laws or finding any violations with respect to
such laws.

ITEM 3.  SOURCE AND AMOUNT OF FUNDS OR OTHER CONSIDERATION.

         Commerce & Industry used its available working capital to purchase the
Additional Shares.


ITEM 4.  PURPOSE OF TRANSACTION.

         The purpose of the acquisition of the Additional Shares by Commerce &
Industry was investment.

A.       ACQUISITION OF ADDITIONAL SECURITIES OF THE ISSUER

         In addition to the purchase of the Additional Shares on the Closing
Date, pursuant to the Amendment, the Investment Agreement was amended to provide
that AIG may, after the Closing Date, still receive or be required to purchase
additional shares of Series A Preferred Stock from the Company as follows:

         If at any time the Company's before or after the Closing Date gross
         losses and allocated loss adjustment expenses associated with claims
         resulting from the Northridge Earthquake should exceed $850 million
         (such excess being referred to herein as the "Excess Loss Amount"), AIG
         shall, if requested in writing by the Company after the Closing Date,
         contribute to the capital of the Company, in whole or in part, an
         amount ("AIG Contribution") up to the lesser of $70 million or the
         Excess Loss Amount. In consideration of the first $20 million of the
         AIG Contribution ("$20 Million Contribution"), the Company shall issue
         to AIG that number of fully paid and nonassessable Earthquake Shares
         having an aggregate liquidation value equal to $20 million. In
         consideration of the remainder of the AIG Contribution following the
         $20 Million Contribution ("Remaining AIG Contribution"), the Company
         shall issue to AIG that number of fully paid and nonassessable
         Earthquake Shares having an aggregate liquidation value equal to (a)
         the amount of the Remaining AIG Contribution plus (b) an amount equal
         to the product of (i) the Remaining AIG Contribution, (ii) 0.65 and
         (iii) the quotient of (A) the number of shares of Common Stock
         beneficially owned or obtainable by AIG and its affiliates by virtue of
         ownership of the shares of Series A Preferred Stock (including any
         additional shares actually issued by virtue of the provision of the
         Certificate of

                              PAGE 7 OF ____ PAGES



<PAGE>   13



         Determination governing the Series A Preferred Stock permitting payment
         of dividends by the issuance of PIK Shares) and the Series A Warrants
         and conversion or exercise thereof divided by (B) the sum of (1) the
         total number of shares of Common Stock of the Company outstanding
         October 17, 1994 plus (2) the number of shares referred to in (A);
         provided, however, that the aggregate liquidation value of any
         Earthquake Shares issued pursuant to the foregoing provisions of the
         Investment Agreement, as amended (without taking into account any
         Series A Preferred Stock issuable as a dividend in kind on any
         outstanding Series A Preferred Stock), shall not exceed $63.2474
         million.

With respect to additional shares of capital stock of the Company which are not
described, AIG may or may not purchase such additional securities at such time
that it is permitted to do so.

(B) THROUGH (J).

         No additional plans or proposals are presently contemplated other than
those described elsewhere in this Form.


ITEM 5.  INTEREST IN SECURITIES OF ISSUER.

         (a) through (b). The information required by these paragraphs is set
forth in Items 7 through 11 and 13 of each of the cover pages of this Amendment
No. 1 to Schedule 13D and is based upon the number of shares of Common Stock
outstanding as of November 1, 1994 (51,472,471) as contained in the Proxy
Statement of the Company, a copy of which was attached to Schedule D as Exhibit
F.

         (c). AIG, American Home, Commerce and Industry, National Union, New
Hampshire, SICO, The Starr Foundation and Starr, and, to the best of each of
their knowledge, the Covered Persons, have not engaged in any transactions in
the Common Stock within the past 60 days other than those transactions described
above occurring on the Closing Date pursuant to the Investment Agreement.

         (d) through (e).  Not applicable.

ITEM 6.  CONTRACTS, ARRANGEMENTS, UNDERSTANDINGS & RELATIONSHIPS
         WITH RESPECT TO SECURITIES OF THE ISSUER.

         Contracts, arrangements, understandings and relationships with respect
to securities of the Company consist of the Investment Agreement, the Series A
Warrant, the Certificate of Determination, the Certificate of Amendment, the
By-Laws, the Quota Share Agreements and the Registration Rights Agreement, each
of which is attached as an exhibit to Schedule D, and the Amendment which is
attached hereto as Exhibit A. All of such contracts, arrangements,
understandings and relationships are

                              PAGE 8 OF ____ PAGES



<PAGE>   14



incorporated in their entirety by reference.

ITEM 7.  MATERIAL TO BE FILED AS EXHIBITS.

         (A)     Amendment No. 1 to Investment and Strategic Alliance Agreement
                 dated as of March 23, 1995 by and between 20th Century
                 Industries and American International Group, Inc.

                              PAGE 9 OF ____ PAGES



<PAGE>   15



                                    SIGNATURE

         After reasonable inquiry and to the best of my knowledge and belief, I
certify that the information set forth in this statement is true, complete and
correct.

Dated:  March 30, 1995

                       AMERICAN INTERNATIONAL GROUP, INC.

                       By: 
                          ----------------------------------
                           Edward E. Matthews
                           Vice Chairman - Finance

                       AMERICAN HOME ASSURANCE COMPANY

                       By: 
                          ----------------------------------
                           Edward E. Matthews
                           Senior Vice President - Finance

                       COMMERCE & INDUSTRY INSURANCE COMPANY

                       By: 
                          ----------------------------------
                           Edward E. Matthews
                           Senior Vice President - Finance

                       NATIONAL UNION FIRE INSURANCE COMPANY OF PITTSBURGH, PA.

                       By: 
                          ----------------------------------
                           Edward E. Matthews
                           Senior Vice President - Finance

                       NEW HAMPSHIRE INSURANCE COMPANY

                       By: 
                          ----------------------------------
                           Edward E. Matthews
                           Vice President

                              PAGE 10 OF ____ PAGES



<PAGE>   16

                                EXHIBIT INDEX
                                --------------


         (A)     Amendment No. 1 to Investment and Strategic Alliance Agreement
                 dated as of March 23, 1995 by and between 20th Century
                 Industries and American International Group, Inc.









<PAGE>   1

                                    EXHIBIT A

                              PAGE 11 OF ____ PAGES



<PAGE>   2



                               AMENDMENT NO. 1 TO
                   INVESTMENT AND STRATEGIC ALLIANCE AGREEMENT

         This Amendment No. 1 to Investment and Strategic Alliance Agreement
("Amendment No. 1") is made and entered into this 23rd day of March, 1995 by and
between 20th Century Industries, a corporation organized and existing under the
laws of the State of California (the "Company"), and American International
Group, Inc., a corporation organized and existing under the laws of the State of
Delaware (the "Investor").

                                 R E C I T A L S

         WHEREAS, the Company and the Investor entered into an Investment and
Strategic Alliance Agreement (the "Agreement") on October 17, 1994, pursuant to
which the Company issued to affiliates of the Investor (a) 200,000 shares of
Series A Convertible Preferred Stock, stated value $1,000 per share, having the
rights, preferences, privileges and restrictions set forth in the Certificate of
Determination of the Company (the "Series A Certificate of Determination")
governing the Series A Convertible Preferred Stock (the "Series A Preferred
Stock"), and (b) 16,000,000 Series A Warrants, each exercisable for one share of
Common Stock, no par value, of the Company ("Common Stock"), subject to
adjustment, having the terms set forth
 in a Warrant Certificate dated December
16, 1994 (the "Warrant Certificate") (the "Series A Warrants");

         WHEREAS, on January 27, 1995, the California Department of Insurance
(the "DOI") and the Company entered into a Stipulation, and, on January 28,
1995, the DOI issued an Order under California Insurance Code Sections 1065.1
and 1065.2, pursuant to which the DOI has required that the Company raise an
additional $50 million of capital for contribution to the Company's insurance
subsidiaries (the "DOI Capital Requirement"), the first $30 million of which
must be raised by March 31, 1995 and the remaining $20 million of which must be
raised by December 31, 1995; and

         WHEREAS, the Company and the Investor have agreed upon a $20 million
capital contribution to the Company by the Investor to fund a portion of the DOI
Capital Requirement, in exchange for which the Company will issue additional
Series A Preferred Shares to the Investor pursuant to Section 4.3 of the
Agreement, and in connection therewith, the Company and the Investor desire to
amend Section 4.3 of the Agreement as set forth herein.

                                A G R E E M E N T

         NOW, THEREFORE, for good and valuable consideration, the receipt of
which is hereby acknowledged, the parties hereto agree as follow:

                              PAGE 12 OF ____ PAGES



<PAGE>   3




         SECTION 1. ISSUANCE OF SERIES A PREFERRED STOCK. Concurrently with the 
execution of this Amendment No. 1, the Investor is contributing $20 million to
the Company pursuant to Section 4.3 of the Agreement to fund a portion of the
DOI Capital Requirement. The Company and the Investor agree that,
notwithstanding the formula set forth in Section 4.3 for determining the number
of Series A Preferred Shares to be issued to the Investor in respect of such
contribution, the Investor and the Company agree that, in consideration for such
contribution, the Company shall issue to the Investor 20,000 Series A Preferred
Shares, having an aggregate liquidation value equal to the amount contributed to
the Company by the Investor.

         SECTION 2. AMENDMENT. In order to memorialize the agreement of the 
Company and the Investor to modify the formula for determining the number of
Series A Preferred Shares to be issued in respect of the Investor's $20 million
contribution to the Company, Section 4.3 of the Agreement is hereby amended to
read in its entirety as follows:

                 "Section 4.3 Investor Contribution and Additional Shares;
                 Adjustment to Series A Warrants Exercise Price. If at any time
                 (before or after the Closing Date) there shall be any Excess
                 Loss Amount as defined above, the Investor shall, if requested
                 writing by the Company after the Closing Date (and subject to
                 the Closing hereunder), contribute to the capital of the
                 Company at the request of the Company, in whole or in part, an
                 amount up to the lesser of (i) $70,000,000 or (ii) the Excess
                 Loss Amount (the "Investor Contribution"). In consideration for
                 the first $20 million of the Investor Contribution pursuant to
                 this Section 4.3 (the "$20 Million Contribution"), the Company
                 shall issue to the Investor that number of fully paid and
                 nonassessable Series A Preferred Shares having an aggregate
                 liquidation value equal to $20 million. In consideration of the
                 contribution of the remainder of the Investor Contribution
                 following the $20 Million Contribution (the "Remaining Investor
                 Contribution"), the Company shall issue to the Investor that
                 number of fully paid and nonassessable Series A Preferred
                 Shares having an aggregate liquidation value equal to (x) the
                 amount of the Remaining Investor Contribution plus (y) an
                 amount equal to the product of, (1) the Remaining Investor
                 Contribution, (2) 0.65 and (3) the quotient of (I) the number
                 of shares of Common Stock beneficially owned or obtainable by
                 the Investor and its affiliates by virtue of ownership of the
                 Series A Preferred Shares (including any additional shares
                 actually issued by virtue of the provision permitting payment
                 of dividends in kind on the Series A Preferred Shares) and the
                 Series A Warrants and conversion or exercise thereof

                              PAGE 13 OF ____ PAGES



<PAGE>   4



         divided by (II) the sum of (A) the total number of shares of Common
         Stock of the Company outstanding at the date of this Agreement plus (B)
         the number of shares referred to in (I); provided, however, that the
         aggregate liquidation value of any Series A Preferred Shares issued
         pursuant to the to this sentence (without taking into account any
         Series A Preferred Shares issuable as a dividend in kind on any
         outstanding Series A Preferred Shares) shall not exceed $63.2474
         million. The amount represented as "(y)" in the above formula is
         designed to represent Investor's proportional share of the Company's
         after-tax loss resulting from the Excess Loss Amount. Successive
         contributions under this Section 4.3 for partial amounts reflecting
         development over time shall be permitted, with minimum cash
         contributions prior to the final contribution being for no less than
         $10 million. In the event that the Excess Loss Amount exceeds
         $95,000,000, the exercise price of the Series A Warrants shall be
         reduced as provided in the Series A Warrants."

         SECTION 3. DEFINED TERMS.  Capitalized terms not otherwise defined 
herein shall have the meanings ascribed to such terms in the Agreement.

         SECTION 4. RECONFIRMATION OF AGREEMENT.  Except as otherwise provided 
herein, all of the terms and provisions of the Agreement shall remain in full
force and effect.

                              PAGE 14 OF ____ PAGES



<PAGE>   5



         SECTION 5. COUNTERPARTS.  This Amendment No. 1 shall be executed in any
number of counterparts, each of which shall be deemed to be one and the same
instrument.

         IN WITNESS WHEREOF, the Company and the Investor have executed this
Amendment No. 1 as of the date first above written.

                           20TH CENTURY INDUSTRIES

                           By: /s/ William L. Mellick
                               -----------------------
                           Name:   William L. Mellick
                           Title:  President & Chief
                                   Executive Officer

                           AMERICAN INTERNATIONAL GROUP, INC.

                           By: /s/ Robert M. Sandler           
                               ------------------------
                           Name:   Robert M. Sandler
                           Title:  Senior Vice President

                           By: /s/ Kathleen E. Shannon
                               -------------------------
                           Name:   Kathleen E. Shannon
                           Title:  Secretary

                              PAGE 15 OF ____ PAGES