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                                                                     Exhibit 4.3

                                    AMENDMENT
                                       TO
                          SHAREHOLDER RIGHTS AGREEMENT

     Amendment, dated as of March 11, 2003 (the "Amendment"), to the Shareholder
Rights Agreement, dated as of November 18, 1998 (the "Rights Agreement"),
between First Bell Bancorp, Inc., a Delaware corporation (the "Company"), and
Registrar and Transfer Company, as Rights Agent (the "Rights Agent").

                                   WITNESSETH:

     WHEREAS, pursuant to Section 26 of the Rights Agreement, the Company may
prior to the Distribution Date (as defined in the Rights Agreement) supplement
or amend the Rights Agreement without the approval of any holders of
certificates representing shares of common stock of the Company; and

     WHEREAS, the Company now desires to amend the Rights Agreement as set forth
in this Amendment, and pursuant to Section 26 of the Rights Agreement, the
Company hereby directs that the Rights Agreement should be amended as set forth
in this Amendment.

     NOW THEREFORE, in consideration of the premises and the mutual agreements
herein set forth, the parties hereby agree as follows:

     1. Amendments to Section 1.

          (a) Section 1 of the Rights Agreement is hereby amended by adding the
     following definitions:

               (ta) "Merger" shall have the meaning set forth in the Merger
          Agreement.

               (ua) "Merger Agreement" shall mean the Agreement and Plan of
          Merger, dated as of March 11, 2003, among the Company, Northwest
          Bancorp MHC, Northwest Bancorp, Inc., Northwest Savings Bank and
          Northwest Merger Subsidiary, Inc., as may be amended from time to
          time.

          (b) The definition of "Acquiring Person" in Section 1(a) of the Rights
     Agreement is hereby amended by inserting the following sentence at the end
     thereof:

          "Notwithstanding the foregoing or any other provision of this
          Agreement to the contrary, none of Northwest Bancorp MHC, Northwest
          Bancorp, Inc., any subsidiary of Northwest Bancorp, Inc. or any other
          Person shall be deemed to be an Acquiring Person by virtue of the
          Merger Agreement as a result of any of (i) the execution and delivery
          of the Merger Agreement, (ii) the consummation of the Merger and (iii)
          the

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          consummation of the other transactions contemplated in the Merger
          Agreement."

     2. Amendment to Section 3(a). Section 3(a) of the Rights Agreement is
hereby amended to add the following sentence at the end thereof:

          "Notwithstanding anything in this Agreement to the contrary, a
          Distribution Date shall not be deemed to have occurred as a result of
          any of (i) the execution and delivery of the Merger Agreement, (ii)
          the consummation of the Merger and (iii) the consummation of the other
          transactions contemplated in the Merger Agreement."

     3. Amendment to Section 7(a). The first sentence of Section 7(a) of the
Rights Agreement is hereby amended to read as follows:

          "Prior to the earlier of (i) the Close of Business on the tenth
          anniversary hereof (the "Final Expiration Date"), (ii) the time at
          which the Rights are redeemed as provided in Section 23 hereof and
          (iii) the Effective Time (as defined in the Merger Agreement) (the
          earlier of (i), (ii) or (iii) being the "Expiration Date"), the
          registered holder of any Rights Certificate may, subject to the
          provisions of Sections 7(e) and 9(c), exercise the Rights evidenced
          thereby in whole or in part at any time after the Distribution Date
          upon surrender of the Rights Certificate, with the form of election to
          purchase on the reverse side thereof duly executed, to the Rights
          Agent at the office of the Rights Agent designated for such purpose,
          together with payment of the aggregate Purchase Price (as hereinafter
          defined) for the total number of Units of Preferred Stock (or,
          following a Triggering Event, other securities, cash or other assets,
          as the case may be) for which such surrendered Rights are then
          exercisable."

     4. Amendment to Section 11. Section 11(a)(ii) of the Rights Agreement is
hereby amended by adding the following sentence at the end thereof:

          "Notwithstanding anything in this Agreement to the contrary, (i) the
          execution and delivery of the Merger Agreement, (ii) the consummation
          of the Merger and (iii) the consummation of the other transactions
          contemplated in the Merger Agreement shall not be deemed to be a
          Section 11(a)(ii) Event and shall not cause the Rights to be adjusted
          or exercisable in accordance with, or any other action to be taken or
          obligation to arise pursuant to, this Section 11(a)(ii)."

     5. Amendment to Section 13. Section 13 of the Rights Agreement is hereby
amended by adding the following sentence at the end thereof:

          "Notwithstanding anything in this Agreement to the contrary, (i) the
          execution and delivery of the Merger Agreement, (ii) the consummation
          of the Merger and (iii) the consummation of the other transactions
          contemplated in the Merger Agreement shall not be deemed to be a
          Section 13 Event and shall not cause the Rights to be adjusted or

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          exercisable in accordance with, or any other action to be taken or
          obligation to arise pursuant to, this Section 13."

     6. Effectiveness. This Amendment shall be deemed effective as of the date
first above written, as if executed on such date. Except as expressly set forth
herein, this Amendment shall not by implication or otherwise alter, modify,
amend or in any way affect any of the terms, conditions, obligations, covenants
or agreements contained in the Rights Agreement, all of which are ratified and
affirmed in all respects and shall continue in full force and effect and shall
be otherwise unaffected.

     7. Governing Law. This Amendment shall be deemed to be a contract made
under the laws of the State of Delaware and for all purposes shall be governed
by and construed in accordance with the laws of such state applicable to
contracts to be made and performed entirely within such state.

     8. Counterparts. This Amendment may be executed in any number of
counterparts, each of which shall for all purposes be deemed an original, and
all of which together shall constitute but one and the same instrument.

     IN WITNESS WHEREOF, the parties have caused this Amendment to be duly
executed as of the day and year first above written.

                                       FIRST BELL BANCORP, INC.

Attest:


/s/ Jeffrey M. Hinds                   By: /s/ Albert H. Eckert, II
-----------------------------------        -------------------------------------
Name: Jeffrey M. Hinds                     Name: Albert H. Eckert, II
Title: Executive Vice President            Title: President


                                       REGISTRAR AND TRANSFER COMPANY

Attest:


/s/ William P. Tatler                  By: /s/ Thomas L. Montrone
-----------------------------------        -------------------------------------
Name: William P. Tatler                    Name: Thomas L. Montrone
Title: Vice President and Assistant        Title: President and Chief Executive
       Secretary                                  Officer