Exhibit 4(b)

                                                             Executed in 6 Parts
                                                            Counterpart No. (  )

                              NATIONAL EQUITY TRUST

                        S&P 500 STRATEGY TRUST SERIES 21

                            REFERENCE TRUST AGREEMENT

      This  Reference  Trust  Agreement  dated October 1, 2003 among  Prudential
Investment Management Services LLC, as Depositor, Prudential Investments LLC, as
Portfolio  Supervisor,  and The Bank of New York, as Trustee, sets forth certain
provisions  in full  and  incorporates  other  provisions  by  reference  to the
document  entitled  "National Equity Trust,  Trust Indenture and Agreement" (the
"Basic  Agreement")  dated February 2, 2000. Such provisions as are set forth in
full herein and such provisions as are  incorporated  by reference  constitute a
single instrument (the "Indenture").

                                WITNESSETH THAT:

      In  consideration  of the  premises  and of the mutual  agreements  herein
contained, the Depositor and the Trustee agree as follows: Part I.

                     STANDARD TERMS AND CONDITIONS OF TRUST

      Subject to the provisions of Part II hereof, all the provisions  contained
in the Basic  Agreement are herein  incorporated  by reference in their entirety
and  shall be deemed  to be a part of this  instrument  as fully and to the same
extent as though said provisions had been set forth in full in this instrument.

A.    Article I, entitled "Definitions," shall be amended as follows:

(i)   Section  1.01-Definitions shall be amended to add the following definition
      at the end thereof:


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      "Portfolio  Supervisor" of the Trust shall have the meaning assigned to it
in Part II of the Reference Trust Agreement.

B.    Article  III,  entitled  "Administration  of  Trust,"  shall be amended as
      follows:

      (i) The third paragraph of Section  3.05-Distribution  shall be amended by
deleting any reference to Depositor and replacing it with Portfolio Supervisor.

      (ii)  Section  3.14-Deferred  Sales  Charge  shall be  amended  to add the
following sentences at the end thereof:

"References to Deferred Sales Charge in this Trust Indenture and Agreement shall
include any Creation and  Development  Fee  indicated  in the  prospectus  for a
Trust.  The  Creation  and  Development  Fee  shall be  payable  on each date so
designated  and in an amount  determined  as specified in the  prospectus  for a
Trust."

C.    Article VIII, entitled "Depositor," shall be amended as follows:

      (i) Section  8.07-Compensation  shall be amended by deleting any reference
to Depositor and replacing it with Portfolio Supervisor.

D.    Article IX, entitled  "Additional  Covenants;  Miscellaneous  Provisions,"
      shall be amended as follows:

      (i) The first  sentence of Section 9.05 - Written  Notice shall be amended
by deleting  the language  "Prudential  Securities  Incorporated  at One Seaport
Plaza,  New York, New York 10292" and replacing it with  "Prudential  Investment
Management LLC at 100 Mulberry Street,  Gateway Center Three, Newark, New Jersey
07102".

                                    Part II.

                      SPECIAL TERMS AND CONDITIONS OF TRUST

        The following special terms and conditions are hereby agreed to:

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A.    The Trust is  denominated  National  Equity Trust,  S&P 500 Strategy Trust
      Series 21.

B.    The Units of the Trust shall be subject to a deferred sales charge.

C.    The publicly  traded  stocks  listed in Schedule A hereto are those which,
      subject to the terms of this  Indenture,  have been or are to be deposited
      in Trust under this Indenture as of the date hereof.

D.    The term "Depositor" shall mean Prudential  Investment Management Services
      LLC.

E.    The term "Portfolio Supervisor" shall mean Prudential Investments LLC.

F.    The aggregate number of Units referred to in Sections 2.03 and 9.01 of the
      Basic Agreement is 125,000 as of the date hereof.

G.    A Unit of the Trust is hereby  declared  initially equal to 1/125,000th of
      the Trust.

H.    The term "First Settlement Date" shall mean October 7, 2003.

I.    The terms "Computation  Day" and  "Record  Date"  mean on the tenth day of
      December 2003, March 2004, June 2004, and September 2004.

J.    The  term  "Distribution  Date"  shall  mean  on  the  twenty-fifth day of
      December 2003, March 2004, June 2004, and September 2004.

K.    The term "Termination Date" shall mean January 5, 2005.

L.    The  Trustee's  Annual Fee shall be $.90 (per 1,000 Units) for  49,999,999
      and below Units  outstanding,  $.84 (per 1,000  Units) for  50,000,000  to
      99,999,999  Units  outstanding,  $.78 (per 1,000 Units) for 100,000,000 to
      199,999,999  Units  outstanding,  and $.66 (per 1,000  Units) for Units in
      excess of 200,000,000  Units. In calculating the Trustee's annual fee, the
      fee applicable to the number of units outstanding shall apply to all units
      outstanding.

M.    The Portfolio Supervisor's portfolio supervisory service fee shall be $.25
      per 1,000 Units.

               [Signatures and acknowledgments on separate pages]


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The Schedule of Portfolio  Securities  in Part A of the  prospectus  included in
this  Registration  Statement for National Equity Trust,  S&P 500 Strategy Trust
Series 21 is hereby incorporated by reference herein as Schedule A hereto.

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                                            PRUDENTIAL INVESTMENT MANAGEMENT
                                            SERVICES LLC,
                                            (Depositor)

                                            By /s/ Richard R. Hoffmann
                                                   Richard R. Hoffmann
                                                   Vice President

                                            PRUDENTIAL INVESTMENTS LLC
                                            (Portfolio Supervisor)

                                            By /s/ Richard R. Hoffmann
                                                   Richard R. Hoffmann
                                                   Vice President


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                                                       THE BANK OF NEW YORK
                                                       Trustee

                                                   By: /s/ Brian Aarons
                                                           Brian Aarons
                                                           Title: Vice President

(SEAL)

ATTEST:

By:      /s/ Dorothy Alencastro
             Dorothy Alencastro
             Title: Assistant Vice President

STATE OF NEW YORK          )
                                            : ss.:
COUNTY OF NEW YORK         )

      I, Emanuel  Lytle,  Jr., a Notary Public in and for the said County in the
state  aforesaid,  do hereby  certify that Brian  Aarons and Dorothy  Alencastro
personally  known to me to be the same persons whose names are subscribed to the
foregoing  instrument  and  personally  known to me to be a Vice  President  and
Assistant Vice President,  respectively of The Bank of New York, appeared before
me this  day in  person,  and  acknowledged  that  they  signed,  sealed  with a
corporate  seal of The Bank of New York,  and delivered  the said  instrument as
their  free  and  voluntary  act as  such  Vice  President  and  Assistant  Vice
President,  respectively,  and as the free and  voluntary act of The Bank of New
York, for the uses and purposes therein set forth.

      GIVEN, under my hand and notarial seal this 1st day of October, 2003.

                                          /s/      Emanuel Lytle, Jr.
                                                   Emanuel Lytle, Jr.
                                                   Notary Public

(SEAL)