Document:

<PAGE>

                                                                    EXHIBIT 10.9
                                                                    ------------

                             SRA International, Inc.

                           SECOND AMENDED AND RESTATED

                            STOCK PURCHASE AGREEMENT

                                 Ernst Volgenau
                                 --------------

                                December 27, 1984

                         as amended through May 19, 2002

<PAGE>

<TABLE>
<CAPTION>
                                      INDEX

                                                                                      Page
                                                                                      ----

<S>      <C>                                                                          <C>
1.       Affirmation of Provisions of Restated Certificate of Incorporation .........   1
2.       Repurchase of Shares upon Death of Shareholder .............................   1
3.       Maintenance of Specified Insurance Policies ................................   2
4.       Alternative Insurance ......................................................   2
5.       Delivery of Shares; Payment of the Purchase Price ..........................   2
6.       Direction to Shareholder's Heirs, Successros, and Legal Representatives ....   2
7.       Transfer of Shares .........................................................   2
8.       Miscellaneous Matters ......................................................   2
  8.1    Agreement to Perform Necessary Acts ........................................   2
  8.2    Counterparts;  Amendments ..................................................   2
  8.3    Successors and Assigns .....................................................   3
  8.4    Validity of Agreement ......................................................   3
  8.5    Other Agreements ...........................................................   3
  8.6    Specific Performance .......................................................   3
  8.7    Notices ....................................................................   3
  8.8    Governing Law ..............................................................   3
</TABLE>

<PAGE>

                              AMENDED AND RESTATED

                            STOCK PURCHASE AGREEMENT

     This AGREEMENT (the "Agreement"), made as of May 19 2002 by and between SRA
International, Inc., a Delaware corporation (the "Corporation"), and Ernst
                                                                     -----
Volgenau, a shareholder of the Corporation (the "Shareholder"), is an amended
--------
and restated revision of a Stock Purchase Agreement dated December 27, 1984, and
thereafter amended on December 31, 1987 and June 30, 1988, and February 20,
1997, and amended and restated on July 30, 1997, between the Corporation and the
Shareholder. This second amended and restated revision supersedes all previous
versions of this Stock Purchase Agreement. Reference herein to the word
"Shareholders" shall mean all shareholders of the Corporation, unless the
context otherwise requires.

                                   WITNESSETH:
                                   -----------

     WHEREAS, the Shareholder holds, and additionally may hold pursuant to
exercise of stock option(s) granted by the Corporation, shares of the Class B
and/or Class A Common Stock (the "Shares") of the Corporation; and

     WHEREAS, the Corporation and the Shareholder wish to provide for the
orderly disposition of the Shares upon the death of the Shareholder;

     NOW, THEREFORE, in consideration of the mutual promises herein set forth,
and for other good and valuable consideration, the parties hereto, each
intending to be legally bound, agree as follows:

     1. Affirmation of Provisions of Restated Certificate of Incorporation. The
        -------------------------------------------------------------------
Corporation and the Shareholder each acknowledges and reaffirms that the Shares
are subject to the provisions and restrictions of the Restated Certificate of
Incorporation, filed March 5, 2002 (the "Restated Certificate"), as the same may
be amended from time to time.

     2. Repurchase of Shares upon Death of Shareholder. The Corporation has
        -----------------------------------------------
purchased, and has continued to pay the premiums for, one or more term life
insurance policies upon the life of Shareholder, as identified on Exhibit A
                                                                  ---------
attached hereto (the "Specified Insurance Policies"), which insurance provides
that upon the death of Shareholder the proceeds of such policy or policies shall
be paid to the Corporation. The Board of Directors of the Corporation has
determined that such proceeds will be used to repurchase that portion, which may
be all, of the Shares which may be purchased for the purchase price as provided
below. The Corporation agrees that, upon the death of Shareholder, the
Corporation shall purchase from the heirs and successors of Shareholder such
Shares in the amount and at the purchase price as provided below. The purchase
price per Share shall be the average closing bid price of the Corporation's
class A common stock (or any successor class of common stock) which is then
publicly traded or listed on a national securities exchange for the thirty (30)
trading days next preceding the date of

<PAGE>

death, as such price is quoted in the Wall Street Journal, or if not so quoted,
on any similar quotation sheet for the market or exchange in which such class A
common stock is traded or listed.

     3. Maintenance of Specified Insurance Policies. The Corporation agrees to
        --------------------------------------------
maintain each Specified Insurance Policy in effect, and continue to pay the
premium on each Specified Insurance Policy, through the date when the premiums
on such policy are no longer fixed at current levels, which date is set forth on
Exhibit A (the respective "Expiration Date"). The Corporation's obligation to
---------
maintain each Specified Insurance Policy, and to repurchase Shares using
proceeds from such Specified Insurance Policy, will cease upon the Expiration
Date of such Specified Insurance Policy.

     4. Alternative Insurance. If for some reason any Specified Insurance Policy
        ----------------------
ceases to be available prior to its Expiration Date, or its premium ceases to be
fixed at current levels prior thereto, the Corporation will, in consultation
with Shareholder, purchase and maintain alternative term insurance for the
duration of the period through such Expiration Date providing the maximum
coverage then available for the same premium.

     5. Delivery of Shares; Payment of the Purchase Price. The Corporation, no
        --------------------------------------------------
later than sixty (60) days following the date of death of the Shareholder, shall
notify the Shareholder's legal representatives of a date, no later than one
hundred eighty (180) days following the date of such Shareholder's death, upon
which date, at the offices of the Corporation in Fairfax, Virginia, certificates
representing the Shares shall be delivered to the Corporation for cancellation,
and the Corporation, shall pay the purchase price therefor. The Corporation, to
the extent funds from insurance policies upon the life of Shareholder are or may
be paid to the Corporation, shall pay the purchase price in cash upon delivery
of the Shares.

     6. Direction to Shareholder's Heirs, Successors, and Legal Representatives.
        ------------------------------------------------------------------------
Shareholder does hereby authorize and direct his heirs, successors, and legal
representatives to comply with the provisions of this Second Amended and
Restated Stock Purchase Agreement.

     7. Transfer of Shares. The Corporation acknowledges that the prior transfer
        -------------------
by the Shareholder of Shares to The Volgenau Joint Revocable Living Trust is not
a "transfer" within the meaning of the Corporation's Restated Certificate or all
previous versions of this Stock Purchase Agreement.

     8. Miscellaneous Matters.
        ---------------------

     8.1 Agreement to Perform Necessary Acts. Each party to this Agreement
         ------------------------------------
agrees to perform any further acts and execute and deliver any documents that
may be reasonably necessary to carry out the provisions of this Agreement.

     8.2 Counterparts; Amendments. This Agreement may be executed in one or more
         -------------------------
counterparts, each of which shall be an original. The provisions of this
Agreement may be waived, altered, amended or repealed, in whole or in part, on
the written consent of the Corporation and the Shareholder.

                                      - 2 -

<PAGE>

     8.3 Successors and Assigns. This Agreement shall be binding on, and shall
         -----------------------
inure to the benefit of, the parties hereto and their respective heirs, legal
representatives, successors and assigns.

     8.4 Validity of Agreement. In the event any provision, or portion thereof,
         ----------------------
of this Agreement is held by a court having proper jurisdiction to be for any
reason unenforceable or invalid, the remaining provisions, or portions thereof,
of this Agreement shall continue to exist and shall remain in full force and
effect.

     8.5 Other Agreements. This Agreement, together with the provisions of the
         -----------------
Restated Certificate, as amended from time to time, set forth all of the
promises, agreements, conditions, understandings, warranties, and
representations between the parties hereto with respect to the Shares, and there
are not promises, agreements, conditions, understandings, warranties, or
representation, oral or written, expressed or implied, between them with respect
to the Shares. This Agreement supersedes all other stock purchase agreements
between the Shareholder and any other Shareholder and the Corporation.

     8.6 Specific Performance. The parties hereto agree that the Shares are
         ---------------------
unique, that failure to perform the obligations provided by this Agreement will
result in irreparable damage, and that specific performance of these obligations
may be obtained by suit in equity.

     8.7 Notices. All notices, requests, demands and other communications under
         --------
this Agreement shall be in writing and shall be deemed to have been duly given
on the date of service if served personally on the party to whom notice is to be
given, or within forty-eight hours after mailing, if mailed to the party to whom
notice is to be given, by first class mail, registered or certified, prepaid and
properly addressed to the party at such party's address set forth as follows or
at any other address that such party may designate by written notice to the
other:

                    If to the Company:               SRA International, Inc.
                                                     4350 Fair Lakes Court
                                                     Fairfax, VA  22033

                    If to the Shareholder:           8302 Summerwood Drive
                                                     McLean, VA 22102

         All notices, requests, demands and other communications under this
Agreement made to the Shareholder's executor, administrator or other
representative shall be addressed to the Shareholder at the Shareholder's
address unless the Corporation is notified in writing of a different address.

     8.8 Governing Law. This Agreement shall be construed in accordance with,
         --------------
and governed by the laws of, the State of Delaware.

                                      - 3 -

<PAGE>

     IN WITNESS WHEREOF, the parties have executed this Agreement as of the 19th
day of May, 2002.

                                            SRA INTERNATIONAL, INC.

                                            By:  /s/ Stephen C. Hughes
                                               --------------------------
                                               Stephen C. Hughes
                                               Chief Financial Officer

                                            SHAREHOLDER:

                                            /s/ Ernst Volgenau
                                            ------------------
                                            Ernst Volgenau

                                      - 4 -

<PAGE>

                                                                       Exhibit A

<TABLE>
<CAPTION>

Summary of Insurance Policies on the Life of Ernst Volgenau Keyman Term
Insurance Policies - SRA International, Inc. Sole Owner and Sole Beneficiary
<S>                                              <C>
Insured                                           Ernst Volgenau

Owner                                             SRA International, Inc.

Beneficiary                                       SRA International, Inc.

Policy Number 1
      Insurance Provider                          Transamerica Occidental Life Insurance Company
      Policy Number                               41775236
      Policy Term                                 June 9, 2000 to June 9, 2010
      Face Amount                                  $  55,500,000
      Annual premium through June 2010             $     294,805

Policy Number 2
      Insurance Provider                          Lincoln Benefit Life Company
      Policy Number                               01T1203279
      Policy Term                                 March 28, 2000 to March 28, 2010
      Face Amount                                  $  20,000,000
      Annual premium through June 2010             $     132,460

Policy Number 2
      Insurance Provider                          Lincoln Benefit Life Company
      Policy Number                               01T1203281
      Policy Term                                 December 28, 1999 to December 28, 2009
      Face Amount                                  $   4,500,000
      Annual premium through June 2010             $      29,535

Combined Face Amount                               $  80,000,000
Combined Annual Premium                            $     456,800
</TABLE>

                                      - 5 -<PAGE>

                                                            EXHIBIT 10.18

                             MODIFICATION AGREEMENT
                             ----------------------

         THIS MODIFICATION AGREEMENT, dated as of April 18, 2002 (the
"Agreement"), made by and among SUNTRUST BANK, a Georgia banking corporation
 ---------
(the "Lender"), SRA INTERNATIONAL, INC., a Delaware corporation (the "Company"),
      ------                                                          -------
SYSTEMS RESEARCH AND APPLICATIONS CORPORATION, a Virginia corporation ("SRA"),
                                                                        ---
SRA TECHNICAL SERVICES CENTER, INC., a Delaware corporation ("STSC", and
                                                              ----
together with the Company and SRA, collectively, the "Original Borrowers"), and
                                                      ------------------
THE MARASCO NEWTON GROUP LTD., a Virginia corporation (the "New Subsidiary") and
                                                            --------------
each other Subsidiary that becomes a party to the Loan Agreement (as herein
defined) in accordance with the provisions set forth therein (together with the
Original Borrowers, collectively, the "Borrowers," and individually, a
                                       ---------
"Borrower"), recites and provides:
 --------
                                    RECITALS
                                    --------

         The Original Borrowers and the Lender are parties to a Loan Agreement,
dated as of August 15, 2001 (as amended, modified or supplemented from time to
time, the "Loan Agreement"). Unless otherwise defined in this Agreement, terms
           --------------
defined in the Loan Agreement shall have the same defined meanings when such
terms are used in this Agreement.

         In accordance with the terms of the Loan Agreement, the Lender agreed
to extend the Loans to the Borrowers. The Revolving Loans are evidenced by a
Revolving Note, dated as of August 15, 2001, made by the Original Borrowers and
payable to the order of the Lender, in the maximum principal amount of
$40,000,000 (as amended, modified, supplemented, extended, renewed or replaced
from time to time, the "Revolving Note"). The Term Loan is evidenced by the
                        --------------
promissory note, dated as of June 28, 1998, made by the Original Borrowers and
payable to the order of the Lender (as amended, modified, supplemented,
extended, renewed or replaced from time to time, the "Term Note," and together
                                                      ---------
with the Revolving Note, the "Notes").
                              -----

         The Loans are secured by (1) the Security Agreement, dated as of August
15, 2001, made by the Original Borrowers in favor of the Lender (as amended,
modified or supplemented from time to time, the "Original Security Agreement")
                                                 ---------------------------
and (2) the Collateral Assignment, Patent Mortgage and Security Agreement, dated
as of August 15, 2001, made by the Original Borrowers in favor of the Lender (as
amended, modified or supplemented from time to time, the "Original Intellectual
                                                          ---------------------
Property Assignment").
-------------------

         The New Subsidiary became a party to the Loan Documents (as defined
below), and assumed all Obligations of the Original Borrowers thereunder, upon
its execution and delivery of the Assumption Agreement, dated as of April 18,
2002, by and between the New Subsidiary and the Lender (as amended, modified or
supplemented from time to time, the "Marasco Assumption"). The New Subsidiary
                                     ------------------
has also executed and delivered the (1) Security Agreement, of even date
herewith, from the New Subsidiary in favor of the Lender (as amended, modified
or supplemented from time to time, the "Marasco Security Agreement") and (2) the
                                        --------------------------
Collateral Assignment, Patent Mortgage and Security Agreement, of even date
herewith, from the New

<PAGE>

Subsidiary in favor of the Lender (as amended, modified or supplemented
from time to time, the "Marasco Intellectual Property Assignment").
                        ----------------------------------------

         The Loan Agreement, the Notes, the Original Security Agreement, the
Original Intellectual Property Assignment, the Marasco Assumption, the Marasco
Security Agreement, the Marasco Intellectual Property Assignment, and each other
Assumption Agreement, Letter of Credit Agreement, Security Agreement, Cash
Management Agreement, and any other documents executed and delivered in
connection with the Loans or the Obligations, are collectively referred to
herein as the "Loan Documents."
               --------------

         The Borrowers have requested that the Lender modify certain provisions
of the Loan Documents, and consent to the New Subsidiary obtaining outside
financing from United Bank. The Lender has agreed to do so, subject to the terms
and conditions of this Agreement. Accordingly, for good and valuable
consideration, the receipt and sufficiency of which are hereby acknowledged, the
Borrowers and the Lender agree as follows:

                                    AGREEMENT
                                    ---------

1.   Incorporation of Recitals.  The Recitals hereto are incorporated herein by
     -------------------------
 reference to the same extent and with the same force and effect as if fully set
 forth herein.

2.   Modifications to Loan Agreement.  The Loan Agreement is modified as
     -------------------------------
 follows:

     (a) All references in the Loan Agreement to "SRA" or "Systems Research and
Applications Corporation" shall be deemed references to Systems Research and
Applications Corporation, a Virginia corporation.

     (b) Notwithstanding the provisions of Section 4.10 of the Loan Agreement,
the Lender acknowledges and agrees that the chief executive office of the New
Subsidiary may be 2801 Clarendon Boulevard, Suite 100, Arlington, Virginia
22201, provided that the New Subsidiary hereby expressly agrees to be subject to
the provisions of Section 5.2 thereof.

     (c) Each reference in the Loan Agreement to (1) the "Borrowers" shall be
deemed to include a reference to the New Subsidiary and (2) the "Loan Documents"
shall be deemed to include a reference to the Marasco Assumption Agreement, the
Marasco Security Agreement and the Marasco Intellectual Property Assignment.

     (d) Except as specifically modified hereby, the Borrowers ratify and
confirm the terms and provisions of the Loan Agreement in all respects, and
agree that such terms and provisions remain in full force and effect.

3.   Modifications to Original Security Agreement.  The Original Security
     --------------------------------------------
 Agreement is modified as follows:

                                       2

<PAGE>

     (a) All references in the Original Security Agreement to "SRA" or "Systems
Research and Applications Corporation" shall be deemed references to Systems
Research and Applications Corporation, a Virginia corporation.

     (b) Section 9(b) of the Original Security Agreement is hereby deleted in
its entirety and replaced with the following:

         "(b) Reimbursement under any liability insurance maintained by
         Borrower pursuant to this Section 9 may be paid directly to the person
         who shall have incurred liability covered by such insurance. In case
         of any loss involving damage to Collateral when Section 9(c) is not
         applicable, Borrower shall make or cause to be made the necessary
         repairs to or replacements of such Collateral, and any proceeds of
         insurance maintained by Borrower pursuant to this Section 9 shall be
         paid to Borrower as reimbursement for the costs of such repairs or
         replacements."

     (c) The reference to Section 16(b) in Section 9(c) of the Original Security
Agreement is hereby amended to be a reference to Section 15(b).

     (d) The reference to Section 16(c) in Section 16 of the Original Security
Agreement is hereby amended to be a reference to Section 15(c).

     (e) Except as specifically modified hereby, the Original Borrowers ratify
and confirm the terms and provisions of the Original Security Agreement in all
respects, and agree that such terms and provisions remain in full force and
effect.

4.   Modifications to Original Intellectual Property Assignment.  The Original
     ----------------------------------------------------------
Intellectual Property Assignment is modified as follows:

     (a) All references in the Original Intellectual Property Assignment to
"SRA" or "Systems Research and Applications Corporation" shall be deemed
references to Systems Research and Applications Corporation, a Virginia
corporation.

     (b) Except as specifically modified hereby, the Original Borrowers ratify
and confirm the terms and provisions of the Original Intellectual Property
Assignment in all respects, and agree that such terms and provisions remain in
full force and effect.

5.   Modifications to Loan Documents.
     -------------------------------

     (a) All references in the Loan Documents to "SRA" or "Systems Research and
Applications Corporation" shall be deemed references to Systems Research and
Applications Corporation, a Virginia corporation.

     (b) Each reference in the Loan Documents to the "Loan Documents" shall be
deemed to include a reference to the Marasco Assumption Agreement, the Marasco
Security Agreement and the Marasco Intellectual Property Assignment. The
Borrowers and the Lender agree that each reference in the Loan Documents to any
particular Loan Document shall be deemed to be a reference to such Loan Document
as amended by this Agreement.

                                       3

<PAGE>

     (c) Except as specifically modified hereby, the Borrowers ratify and
confirm the terms and provisions of the Loan Documents in all respects, and
agree that such terms and provisions remain in full force and effect.

6.   Consent to Financing.
     --------------------

     (a) Pursuant to the provisions of Sections 6.2 and 6.9 of the Loan
Agreement, the Lender hereby consents to the New Subsidiary obtaining outside
financing from United Bank (the "Approved Financing"), and to SRA guaranteeing
                                 ------------------
the indebtedness and obligations of the New Subsidiary thereunder, provided,
                                                                   --------
however, that the consent of the Lender given hereunder is subject to the
-------
following conditions: (a) the total indebtedness of the New Subsidiary under the
Approved Financing shall not exceed $500,000 at any one time outstanding, (b)
the indebtedness and obligations of the New Subsidiary under the Approved
Financing shall be unsecured, (c) the guaranty of SRA shall be limited to only
the New Subsidiary's indebtedness and obligations under the Approved Financing,
and (d) the Approved Financing shall have a maturity occurring no later than
that date which is 30 days after the expiration of the period during which the
New Subsidiary is permitted to operate as a separate subsidiary under the
provisions of Section 6.6 of the Agreement and Plan of Merger, dated as of
December 5, 2001, by and between, among others, SRA and the New Subsidiary, as
the same may be amended, modified or supplemented from time to time.

     (b) The consent of the Lender given hereunder shall not constitute an
approval, either express or implied, of any other transaction or a waiver or
approval of any other provision of the Loan Agreement or any other Loan
Document, nor shall it create any obligation, express or implied, of the Lender
to approve any future transaction or waiver or approval of any other covenant,
term or provision of the Loan Agreement or any other Loan Document. The Lender
shall be entitled to require strict compliance by the Borrowers with the Loan
Agreement and the other Loan Documents, notwithstanding the limited, express
approval contained herein, and nothing herein shall be deemed to establish a
course of action or dealing with respect to requests by the Borrowers for future
approvals or consents.

7.   Conditions Precedent.  The following are conditions precedent to the
     --------------------
effectiveness of this Agreement:

     (a) The Borrowers shall execute and deliver this Agreement, in form and
substance satisfactory to the Lender;

     (b) No event shall have occurred and be continuing that constitutes an
Event of Default, or that would constitute an Event of Default but for the
requirement that notice be given or that a period of notice elapse, or both; and

                                       4

<PAGE>

     (c) All documents delivered pursuant to this Agreement must be in form and
substance satisfactory to the Lender and its counsel, and all legal matters
incident to this Agreement must be satisfactory to the Lender's counsel.

8.   Miscellaneous.
     -------------

     (a) All representations and warranties made by the Borrowers in the Loan
Documents are incorporated by reference in this Agreement and are deemed to have
been repeated as of the date of this Agreement with the same force and effect as
if set forth in this Agreement; provided, however, that any representation or
warranty relating to any financial statements shall be deemed to be applicable
to the financial statements most recently delivered to the Lender in accordance
with the provisions of the Loan Documents.

     (b) The Borrowers agree that nothing in this Agreement shall require the
Lender to grant any further modifications of the Loan Documents.

     (c) The Borrowers shall pay all costs and expenses incurred by the Lender
in connection with this Agreement, including, but not limited to, reasonable
attorneys' fees.

     (d) The Borrowers acknowledge and agree that there are no defenses,
counterclaims or setoffs against any of their respective obligations under the
Loan Documents.

     (e) The Borrowers agree that a default by any of them under this Agreement
shall constitute an Event of Default under the Loan Agreement.

     (f) This Agreement shall be governed by the laws of the Commonwealth of
Virginia, without reference to conflict of laws principles.

                         [SIGNATURES ON FOLLOWING PAGE]

                                       5

<PAGE>

         IN WITNESS WHEREOF, the parties have caused this Agreement to be
executed on the day and year first written above.

                                      LENDER:
                                      ------

                                      SUNTRUST BANK, a Georgia banking
                                      corporation

                                      By:      /s/ Nancy R. Petrash
                                               -------------------------------
                                      Name:    Nancy R. Petrash
                                               -------------------------------
                                      Title:   Director
                                               -------------------------------

                                      COMPANY:
                                      -------

                                      SRA INTERNATIONAL, INC., a Delaware
                                      corporation

                                      By:      /s/ Stephen C. Hughes
                                               -------------------------------
                                      Name:    Sr. VP; CFO
                                               -------------------------------
                                      Title:   Stephen C. Hughes
                                               -------------------------------

                                      SRA:
                                      ---

                                      SYSTEMS RESEARCH AND APPLICATIONS
                                      CORPORATION, a Virginia corporation

                                      By:      /s/ Stephen C. Hughes
                                               -------------------------------
                                      Name:    Stephen C. Hughes
                                               -------------------------------
                                      Title:   Sr. VP & CFO
                                               -------------------------------

                     [SIGNATURES CONTINUE ON FOLLOWING PAGE]

                                       6

<PAGE>

                                      STSC:
                                      ----

                                      SRA TECHNICAL SERVICES CENTER, INC.,
                                      a Delaware corporation

                                      By:      /s/ Stephen C. Hughes
                                               -------------------------------
                                      Name:    Stephen C. Hughes
                                               -------------------------------
                                      Title:   Sr. VP & CFO
                                               -------------------------------

                                      NEW SUBSIDIARY:
                                      --------------

                                      THE MARASCO NEWTON GROUP LTD.,
                                      a Virginia corporation

                                      By:      /s/ Amy L. Marasco
                                               -------------------------------
                                      Name:    Amy L. Marasco
                                               -------------------------------
                                      Title:   President
                                               ----------------------------

                                       7

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