<PAGE>


                                                                   Exhibit 10.23


                      -----------------------------------------

                                ASSIGNMENT OF LEASES

                        ARLINGTON SQUARE LIMITED PARTNERSHIP,
                           a Virginia limited partnership
                                     (Assignor)

                                         and

                        METROPOLITAN LIFE INSURANCE COMPANY,
                               a New York corporation
                                     (Assignee)

                      ------------------------------------------

                      Dated:            As of November 25, 1998

                      Location:         4401 N. Fairfax Drive

                      Description:      Parcel A, Arlington
                                        Square, Deed Book 2210,
                                        Page 994
                      County:           Arlington
                      State:            Virginia

                      ------------------------------------------
                      PREPARED BY AND AFTER RECORDING AND
                      RETURN TO:

                      Mayer, Brown & Platt
                      2000 Pennsylvania Avenue, N.W., Suite 6500
                      Washington, D.C. 20006
                      Attention: Keith J. Willner, Esq.

                                    RPC No.: 14017016



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                             ASSIGNMENT OF LEASES

                                 DEFINED TERMS

-------------------------------------------------------------------------------
EXECUTION DATE: As of November 25, 1998
-------------------------------------------------------------------------------
LOAN: A first deed of trust loan in an amount of $21,500,000.00 from Assignee
      to Assignor
------------------------------------------------------------------------------
ASSIGNOR & ADDRESS:          Arlington Square Limited Partnership,
                             a Virginia limited partnership
                             c/o The Washington Corporation
                             4650 East-West Highway, Suite 251
                             Bethesda, Maryland 20814
                             Attention: William N. Demas
-------------------------------------------------------------------------------
ASSIGNEE & ADDRESS:          Metropolitan Life Insurance Company,
                             a New York corporation
                             200 Park Avenue, 12th Floor
                             New York, New York 10166
                             Attention: Senior Vice-President
                                        Real Estate Investments

          and:               Metropolitan Life Insurance Company
                             One Madison Avenue
                             New York, New York 10010-3690
                             Attention:  Vice-President and Investment Counsel
                                         Real Estate Investments
-------------------------------------------------------------------------------
NOTE: Promissory Note executed by Assignor in favor of Assignee in the amount of
the Loan dated as of the Execution Date, together with all extensions, renewals,
modifications, restatements and amendments thereof.
-------------------------------------------------------------------------------
DEED OF TRUST: Deed of Trust, Security Agreement and Fixture Filing dated as of
the Execution Date, executed by Assignor to secure repayment of the Note,
together with all extensions, renewals, modifications, restatements and
amendments thereof. The Deed of Trust will be recorded in the records of the
County in which the Property (defined below) is located.

         THIS ASSIGNMENT OF LEASES (this "Agreement") is entered into by
Assignor as of the Execution Date in favor of Assignee and affects the Land
described in EXHIBIT A attached to this Agreement. Capitalized terms which are
not defined in this Agreement shall have the respective meanings set forth in
the Deed of Trust.

                                    RECITALS

         A. Assignee has loaned or will loan to Assignor the Loan which is
evidenced by the Note. The payment of the Note is secured by the Deed of Trust
which encumbers Assignor's interest in the real property described in EXHIBIT A
attached to this Agreement (the "LAND" and Assignor's interest in the
improvements and personal property and equipment situated on the Land (the
"IMPROVEMENTS"; collectively with the Land, the "PROPERTY"); and


<PAGE>

          B. Assignor desires to absolutely, presently and unconditionally
assign to Assignee all of its right, title and interest in and to (i) all leases
which now exist that affect the Property, (ii) all leases entered into after the
date of this Agreement, (iii) all lease extensions, modifications, amendments,
expansions and renewals of the leases described in (i) and (ii), and (iv) all
guarantees of tenants' obligations and extensions, modifications, amendments and
renewals of any guarantees of any of the leases. The documents described in this
RECITAL B are collectively referred to as the "LEASES".

          NOW THEREFORE, in consideration of the Recitals and for good and
valuable consideration, Assignor agrees with Assignee and its successors and
assigns as follows:

          1. PAYMENT OF NOTE. Assignor desires to secure (a) the timely payment
of the principal of and interest on the Note and all other indebtedness secured
by the Deed of Trust; and (b) the full compliance with the terms, conditions,
covenants and agreements contained in the Note, the Deed of Trust and the other
documents executed by Assignor in connection with the Loan.

          2. PRESENT AND ABSOLUTE ASSIGNMENT OF LEASES. Assignor absolutely,
presently and unconditionally grants, assigns and transfers to Assignee all of
Assignor's right, title and interest in and to the Leases. This grant includes
without limitation: (a) all rent payable under the Leases; (b) all tenant
security deposits held by Assignor pursuant to the Leases; (c) all additional
rent payable under the Leases; (d) all proceeds of insurance payable to Assignor
under the Leases and all awards and payments on account of any taking or
condemnation; and (e) all claims, damages and other amounts payable to Assignor
in the event of a default under or termination of any of the Leases, including
without limitation all of Assignor's claims to the payment of damages arising
from any rejection by a tenant of any Lease under the Bankruptcy Code as amended
from time to time. All of the items referred to in this SECTION 2 are
collectively referred to in this Agreement as the "INCOME".

          3. NO CANCELLATION OR MODIFICATION OF LEASES. Assignor covenants
and agrees that it shall not, without the express written consent of Assignee,
(a) enter into or extend any Lease unless the Lease complies with the Leasing
Guidelines which are attached to the Deed of Trust as EXHIBIT B or (b) cancel or
terminate any Leases (except in the case of a default) unless Assignor has
entered into new Leases covering all of the premises of the Leases being
terminated or surrendered, or (c) modify or amend any Leases in any material way
or reduce the rent or additional rent, or (d) consent to an assignment of the
tenant's interest or to a subletting of any Lease unless the tenant remains
liable under the Lease following the assignment or subletting, or (e) accept
payment of advance rents or security deposits in an amount in excess of one
month's rent, or (f) enter into any Leases that contain any option to purchase
the Property.

          If any of these acts described in this SECTION 3 are done without the
consent of Assignee, at the option of Assignee, they shall be of no force or
effect and shall constitute a breach of the terms of this Agreement and of the
Deed of Trust.


                                       2

<PAGE>

         4. SPECIFIC COVENANTS OF ASSIGNOR. Assignor covenants and agrees:

                  (a) To perform fully all material obligations, duties, and
         agreements of landlord under the Leases.

                  (b) To deposit all security deposits delivered by tenants in
         connection with the Leases in accordance with applicable law;

                  (c) At Assignor's sole cost and expense, to appear in and
         defend any action or proceeding arising under the Leases or which is
         connected with the obligations, duties or liabilities of landlord,
         tenant or any guarantor and to pay all costs and expenses of Assignee,
         including reasonable attorneys' fees, in any action or proceeding in
         which Assignee may appear;

                  (d) If Assignor fails to make any payment or to do any acts
         required by this Agreement, then Assignee may in its sole discretion
         and without notice to Assignor perform Assignor's obligations under the
         Leases as Assignee may deem necessary, at Assignor's cost and expense.
         These acts may include without limitation appearing in and defending
         any proceeding connected with the Leases, including without limitation
         any proceedings of any tenants under the Bankruptcy Code. No action by
         Assignee shall release Assignor from its obligation under this
         Agreement. Assignor irrevocably appoints Assignee its true and lawful
         attorney to exercise it rights under this Agreement, which appointment
         is coupled with an interest and with full power of substitution;

                  (e) To pay immediately upon demand all sums expended by
         Assignee under this Agreement, together with interest at the Default
         Rate (as defined in the Note), if any. These expenditures shall be
         secured by the Deed of Trust;

                  (f) If a petition under the Bankruptcy Code shall be filed by
         or against Assignor and Assignor, as landlord, shall determine to
         reject any lease pursuant to Bankruptcy Code Section 365(a), then
         Assignee shall have the right, but not the obligation, to demand
         that Assignor assume and assign the lease to Assignee; and

                  (g) Assignee's rights under this Agreement may be exercised
         either independently of or concurrently with any other right in this
         Agreement, the Deed of Trust or in any other document securing the
         Note. No action taken by Assignee under this Agreement shall cure or
         waive any default nor affect any notice under the Deed of Trust.

         5. LEASING OF PROPERTY. Assignor covenants and agrees to use all
reasonable efforts to keep the Property leased at fair market rental and,
upon demand, to confirm in writing the assignment to Assignee of all
subsequent Leases of the Property upon the terms set forth in this Agreement.
Notwithstanding the preceding sentence, the terms and provisions of this
Agreement shall apply automatically to any Leases entered into after the
Execution Date.


                                       3

<PAGE>

         6. REPRESENTATIONS AND WARRANTIES. Assignor makes the following
representations and warranties in connection with the Leases:

                  (a) There are no leases or occupancy agreements affecting the
         Property except the leases and amendments listed on EXHIBIT B hereto
         and Assignor has delivered to Assignee true, correct and complete
         copies of all leases, including amendments (collectively, "EXISTING
         LEASES" and all guaranties and amendments of guaranties given in
         connection with the Existing Leases (the "GUARANTIES").

                  (b) All Existing Leases and Guaranties are in full force and
         effect without any oral or written modification except as set forth in
         writing in the copies delivered to Assignee.

                  (c) There are no defaults by Assignor under the Existing
         Leases and Guaranties and, to the best knowledge of Assignor, there are
         no defaults by any tenants under the Existing Leases or any guarantors
         under the Guaranties. The Existing Leases and the Guaranties are in
         full force and effect.

                  (d) To the best knowledge of Assignor, none of the tenants now
         occupying 10% or more of the Property or having a current lease
         affecting 10% or more of the Property is the subject of any bankruptcy,
         reorganization or insolvency proceeding or any other debtor-creditor
         proceeding.

                  (e) Except only for rent and additional rent for the current
         month, Assignor has not accepted under any of the Leases any payment of
         advance rent, additional rent or security deposit in an amount that is
         more than one month's rent and additional rent.

                  (f) Assignor has deposited all security deposits, if any,
         delivered in connection with the Existing Leases in accordance with
         applicable law.

                  (g) No tenant under any Existing Lease has asserted any
         defense, set-off or counterclaim with respect to its tenancy or its
         obligations under its lease, and no such defense, set-off or
         counterclaim exists.

                  (h) There are no unfulfilled landlord obligations due to
         tenants for tenant improvements, moving expenses or rental concessions
         or other matters, and all credits required to be paid or contributed by
         Assignor under the Existing Leases have been paid or contributed in
         full; provided that amounts described in Section 6(g) of the lease with
         the United States of America described more fully on EXHIBIT B hereto
         are, at the tenant's request, being held by Allied Capital Commercial
         Corporation for the benefit of the tenant in lieu of delivering such
         amounts directly to tenant.

                  (i) None of the Leases, Income or Rents and Profits have been
         assigned, pledged, hypothecated or otherwise encumbered or transferred
         by Assignor except to the extent provided in the Loan Documents.


                                       4

<PAGE>

                  (j) Assignor has not done any act which might prevent Assignee
         from exercising its rights under this Agreement.

         7. LICENSE TO COLLECT MONIES UNTIL DEFAULT BY ASSIGNOR. So long as no
Event of Default (as defined in the Deed of Trust) exists and so long as there
is no default by Assignor under this Agreement or under any of the Leases (all
of the foregoing are collectively referred to as a "DEFAULT"), Assignor shall
have a license to receive and use all Income. Upon the occurrence of a Default,
whether or not legal proceedings have commenced, and without regard to waste,
adequacy of security for the Secured Indebtedness or solvency of Assignor, the
license herein granted shall automatically expire and terminate, without notice
by Assignee (any such notice being hereby expressly waived by Assignor).
Assignee shall thereupon and thereafter have all right, power and authority to
exercise and enforce any and all of its rights and remedies as provided herein,
under any of the other Loan Documents or by law or in equity. Such rights and
remedies shall expressly include the right to exercise and enjoy, in Assignee's
sole and absolute discretion, all of the rights, powers and benefits under the
Leases assigned to Assignee hereunder, it being understood and agreed that
Assignee shall not be liable, and Assignor shall at all times remain solely
liable, to the tenants to perform any and all duties or obligations owing to
such tenants under the Leases, unless Assignee shall elect, in its sole and
absolute discretion, to undertake such duties or obligations.

         8. ENTRY BY ASSIGNEE AND RECEIVER. Assignee is authorized either in
person or by agent, with or without bringing any action or proceeding or having
a receiver appointed by a court, (a) to enter upon, take possession of, manage
and operate the Property and collect the Income, and (b) to make, enforce,
modify, and accept the surrender of the Leases. Assignee is authorized to take
these actions either with or without taking possession of the Property. In
connection with this entry, Assignor authorizes Assignee to perform all acts
necessary for the operation and maintenance of the Property. Assignee may sue
for or otherwise collect all Income, including those past due and unpaid, and
apply the Income, less costs and expenses of operation and collection, including
reasonable attorneys' fees, to the indebtedness secured by the Deed of Trust in
such order as Assignee may determine. Assignee's exercise of its rights under
this SECTION 8 shall not be deemed to cure or waive any Default.

         9. INDEMNIFICATION. Assignor shall indemnify Assignee against and hold
it harmless from any and all liability, claims, loss or damage which it may
incur under the Leases or under this Agreement.

         10. MORTGAGEE IN POSSESSION. To the fullest extent permitted by law,
neither the assignment of Income to Assignee nor the exercise by Assignee of any
of its rights or remedies under this Agreement, including without limitation,
the entering into possession or the appointment of a receiver shall be deemed to
make Assignee a "mortgagee-in-possession" or otherwise liable with respect to
the Property. Although Assignee has the right to do so, it shall not be
obligated to perform any obligation under the Leases by reason of this
Agreement. To the fullest extent permitted by law, neither this Agreement nor
any action or inaction on the part of Assignee shall constitute an assumption on
the part of Assignee of any obligation or liability under any of the Leases.


                                       5

<PAGE>

          11. RECONVEYANCE AND TERMINATION. Upon the payment in full of the
Loan, as evidenced by the recording of an instrument of full reconveyance of the
Deed of Trust, this Agreement shall be void and of no effect.

          12. TENANTS ENTITLED TO RELY ON ASSIGNEE'S REQUESTS. Assignor
irrevocably authorizes and directs the tenants and their successors, upon
receipt of any written request of Assignee stating that a Default exists, to pay
to Assignee the Income due and to become due under the Leases. Assignor agrees
that the tenants shall have the right to rely upon any such statement without
any obligation to inquire as to whether a Default actually exists and regardless
of any claim of Assignor to the contrary. Assignor agrees that it shall have no
claim against the tenants for any Income paid by the tenants to Assignee. Upon
the curing of all Defaults, Assignee shall give written notice to the tenants to
recommence paying the rents to Assignor.

         13. SUCCESSORS AND ASSIGNS. This Agreement shall be binding upon the
successors and assigns of Assignor and shall inure to the benefit of and be
enforceable by Assignee, its successors and assigns and any trustee appointed
for the benefit of the holder of the Note. If more than one person, corporation,
partnership or other entity shall execute this Agreement, then the obligations
of the parties executing the Agreement shall be joint and several.

          14. EXCULPATION. The provisions of Section 9.01 of the Deed of Trust
are incorporated herein by this reference to the fullest extent as if the text
of such section were set forth in its entirety herein.

          15. NOTICES. All notices pursuant to this Agreement shall be given in
accordance with the Notice provision of the Deed of Trust, which is incorporated
into this Agreement by this reference.

          16. GOVERNING LAW. This Agreement and the rights and obligations of
the parties under this Agreement shall in all respects be governed by, and
construed and enforced in accordance with, the laws of the State in which the
Property is located, without regard to conflict of laws principles.

          17. MISCELLANEOUS. This Agreement may be modified, amended, waived, or
terminated only by an instrument in writing signed by the party against which
enforcement of such modification, amendment, waiver, or termination is sought.
No failure or delay in exercising any of these rights shall constitute a waiver
of any Default. Assignor, at its expense, will execute all documents and take
all action that Assignee from time to time may reasonably request to preserve
and protect the rights provided under this Agreement. The headings in this
Agreement are for convenience of reference only and shall not expand, limit or
otherwise affect the meanings of the provisions. This Agreement may be executed
in several counterparts, each of which shall be an original, but all of which
shall constitute one document.

              [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK]


                                       6

<PAGE>


         IN WITNESS WHEREOF, this Assignment of Leases is executed under seal as
of the Execution Date.

WITNESS:


                                    ARLINGTON SQUARE LIMITED PARTNERSHIP,
                                    a Virginia limited partnership

                                    By: Arlington Square, Inc.,
                                        a Virginia,corporation
                                        its general partner


Briscilla D Okay                    By:     /s/ William N. Demas    [Seal]
----------------                        ---------------------------
                                              William N. Demas
                                              President


                                       7

<PAGE>


STATE OF District of          )
         ------------         )
                              )         ss.
COUNTY OF Columbia            )
         ------------         )

On the 24th day of November in the year 1998 before me, the undersigned, a
notary public in and for said state, personally appeared William N. Demas,
President of Arlington Square, Inc., the general partner of Arlington Square
Limited Partnership, who is personally known to me or proved to me on the basis
of satisfactory evidence to be the individual whose name is subscribed to the
within instrument and acknowledged to me that he executed the same on behalf of
and in his capacity as President of said corporation, the general partner of
said partnership.


                                                       /s/ VERONICA JENKINS
                                                    --------------------------


My commission expires: ____________________


                      VERONICA JENKINS
              NOTARY PUBLIC, DISTRICT OF COLUMBIA
              MY COMMISSION EXPIRES APRIL 30, 2003


                                       8

<PAGE>


                                    EXHIBIT A

                          LEGAL DESCRIPTION OF THE LAND

         Parcel A, ARLINGTON SQUARE, as duly dedicated, platted, and recorded in
Deed Book 2210, page 994, among the land records of Arlington County, Virginia.


<PAGE>


                                    EXHIBIT B

                                  LIST OF LEASES

1.       Lease dated June 22, 1998 between Assignor and the United States of
         America, as amended by Supplemental Lease Agreement dated October 20,
         1998.

2.       Lease dated September 16, 1998 between Assignor and the Department of
         the Interior U.S. Fish and Wildlife Service.