EXHIBIT 5.1
 
              [LETTERHEAD OF PATTERSON, BELKNAP, WEBB & TYLER LLP]


                                                               May 7, 1997


       Dime Bancorp, Inc.
       589 Fifth Avenue
       New York, New York  10017

       Dear Sirs:

                 As set forth in the Registration Statement on Form S-8
       ("Registration Statement") proposed to be filed by Dime Bancorp, Inc.
       (the "Company") on May 7, 1997 under the Securities Act of 1933, as
       amended, relating to 350,000 shares (the "Shares") of common stock, par
       value $.01 per share, of the Company to be issued pursuant to the Dime
       Bancorp, Inc. 1997 Stock Incentive Plan for Outside Directors (the
       "Plan"), certain legal matters in connection with the Shares offered
       pursuant to the Plan are being passed upon for the Company by this
       firm. At your request, this opinion of counsel is being furnished to you
       for filing with the Registration Statement.

                 In our capacity as counsel in this connection, we have
       familiarized ourselves with the Amended and Restated Certificate of
       Incorporation and Bylaws, each as amended to date, of the Company and
       have examined the originals, or copies certified or otherwise identified,
       of the Plan, corporate records of the Company, certificates of public
       officials and representatives of the Company, statutes and other
       instruments and documents as the basis for the opinion hereinafter
       expressed.
 
                 On the basis of the foregoing, we are of the opinion that the
       Shares, when issued and sold pursuant to the provisions of the Plan for a
       consideration at least equal to the par value of the Shares, will be duly
       authorized, validly issued, fully paid and nonassessable.

 
May 7, 1997
Page 2


                 We hereby consent to the filing of this opinion letter with the
       Registration Statement.

                                      PATTERSON, BELKNAP, WEBB & TYLER LLP



                                      By:  /s/ Douglas E. Barzelay
                                           -----------------------------------
                                           Douglas E. Barzelay