<PAGE>
 
                                                                   Exhibit 10.21
                                                                   -------------

                            GRC INTERNATIONAL, INC.
                             EMPLOYMENT AGREEMENT
                        (SENIOR VICE PRESIDENT & above)

THIS EMPLOYMENT AGREEMENT is made in Vienna, Virginia as of April 29, 1996 by 
                                                            --------------
and between Ronald B. Alexander (hereinafter referred to in the first person ofr
            -------------------
as "Employee") and GRC International, Inc., a corporation with its principal 
offices at 1900 Gallows Road, Vienna, Virginia 22182 ("Company"). The term 
"Company" shall also include any parent, subsidiary or affiliate of the Company.
As a condition to, and in consideration of, the Company's employment of 
Employee, the parties mutually agree as follows:


1.    DUTIES.
      ------

(a)   I agree to work for the Company in the capacity set forth in item 1(a) of 
Exhibit A attached hereto. My duties will include all those generally associated
with said position, subject to the direction and assignment of the Company's 
Board of Directors. The duties assigned to me shall be performed at the place of
employment specified in item 1(b) of Exhibit A or at such other location as the 
Board of Directors may determine is in the best interest of the Company. All of 
my working time and energies shall be devoted to the foregoing duties. I will 
inform the Company, in writing, if I engage in any outside business activity, 
and I will obtain the prior written approval of the Company, if I engage in any 
outside business activity which (i) requires the use of skills for which I was
hired by the Company or the use of skills attained during the course of my 
employment with the Company or (ii) would, in the opinion of the Company, 
compete with or conflict with my employment with the Company. While employed by 
the Company, absent the expressed, prior written authorization of the Company's 
Board of Directors, I will not, directly or indirectly, engage in any activity 
competitive with or adverse to the Company's business or welfare, whether alone,
as a partner of any partnership or joint venture or as an officer, director, 
employee, or holder of 5% or more of any class of stock, of any corporation.

(b)   I agree that for a period of one year immediately following termination 
(voluntary or otherwise) of my employment with the Company, I will not interfere
with the business of the Company by inducing an employee to leave the Company's 
employment, by inducing a consultant to sever the consultant's relationship with
the Company, or by inducing a customer to sever the customer's relationship with
the Company.

(c)   This Agreement cancels and replaces in their entirety any and all previous
employment agreements entered into between me and the Company or any of its 
subsidiaries.

2.    INTELLECTUAL PROPERTY.
      ---------------------

(a)   In this Agreement, (i) "Intellectual Property" means any patent,
trademark, copyright, semiconductor mask right, trade secret, invention,
discovery, design, idea or improvement (whether or not any of the foregoing are
patentable, protectable by copyright, or otherwise protectable), and (ii) the
word "made", when used with "Intellectual Property", means made, devised,
developed, conceived or reduced to practice. Exhibit B to this Agreement
contains a complete list of all Intellectual Property I consider proprietary to
me, and, during my employment with the Company, I agree to update Exhibit B from
time to time as may be necessary to keep it current. I will not incorporate or
permit to be incorporated into any work performed for or on behalf of the
Company any Intellectual Property proprietary to me or any third party.

(b)   I will disclose to the Company all Intellectual Property made by me, alone
or with others, during any period of employment with the Company. All such 
disclosures shall be reviewed by the Company in confidence to determine any 
issues which may arise.
<PAGE>
 
(c)   I will assign to the Company all right, title and interest in and to all 
Intellectual Property made at any time by me alone or with others during or 
after my employment with the Company, if such Intellectual Property was made 
using Company equipment, supplies, facilities, or trade secret information, or 
such Intellectual Property either (i) relates at the time of conception or 
reduction to practice of the invention to the Company's business, or actual or 
demonstrably anticipated research or development of the Company; or (ii) results
from any work performed by me for the Company.  All Intellectual Property 
subject to this paragraph shall remain Company property whether or not so 
disclosed or assigned to the Company.  I will cooperate fully with the Company 
during and after employment in accomplishing the intent of this provision and 
execute such instruments and documents reasonably requested by the Company, in 
order to more fully vest in the Company all ownership rights in the 
Intellectual Property.  In addition, I irrevocably appoint the Company and each 
of its officers as my agent and attorney-in-fact to act in my name and stead to 
execute and file any documents and to do all other lawfully permitted actions to
further the prosecution, issuance and enforcement of patents, copyrights and 
other proprietary rights with the same force and effect as if executed and 
delivered by me.

(d)   The provisions of the foregoing Section 2(c) shall not apply to an 
invention developed by me entirely on my own time without using Company 
equipment, supplies, facilities, or trade secret information except for those 
inventions that either (i) relate at the time of conception or reduction to 
practice of the invention to the Company's business, or actual or demonstrably 
anticipated research or development of the Company; or (ii) result from any work
performed by me for the Company.

3.    PROPRIETARY INFORMATION.  I understand that in the course of my employment
      -----------------------
with the Company, I will be making use of, acquiring or adding to proprietary 
and/or confidential information and materials of the Company or of other parties
("Proprietary Information").  I will not disclose or use any Proprietary 
Information either during or after my employment with the Company, except to the
extent expressly authorized in writing by an officer of the Company.  The 
following are some examples of Proprietary Information, even if not marked or 
identified as such:

(i)   Computer software of all kinds, source and object codes, algorithms, 
coding sheets, compilers, assemblers, design concepts, routines and subroutines,
and all related documents and materials;

(ii)  Business practices, marketing techniques, mailing lists, purchasing 
information, price lists, pricing policies, quoting procedures, customer and 
prospective customer lists and information, and all materials or information  
relating to the manner in which the Company does business.

(iii) Discoveries, concepts and ideas, whether or not patentable, protectable by
copyright, or otherwise protectable, trade secrets, "know how", production 
processes, research and development activities, and information on products or
programs.

(iv)  Financial information, cost structure, bidding strategy, salary structure,
and such other information not in the public domain as may be helpful to
competitors or harmful to the Company, its customers or employees.

(v)   Any other information, materials or documents related to the business or 
activities of the Company which are not generally known to others engaged in 
similar businesses or activities; and

(vi)  All ideas which are derived from my access to or knowledge of any of the 
above.

4.    CONFLICTS OF INTEREST.  I have read and understood the Company's Corporate
      ---------------------
Standards of Conduct, and while employed by the Company, I agree to abide by
said Standards of Conduct, as the same may be amended from time to time, and to
complete the Company's Ethics Questionnaire as required by the Company from time
to time. Except as fully disclosed in a document attached to this agreement, I
am not a party to any agreement or understanding with any other person or
business, nor am

                                     -2- 

<PAGE>
 
I subject to any other legal restriction or obligation, which would in any way 
prohibit, impede or hinder my employment with the Company or the performance of 
my duties in the course of such employment.

5.    COMPENSATION.
      ------------

(a)   During the term of my employment hereunder, the Company shall pay me the 
annual salary set forth in Exhibit A, Item 3(a) ("Gross Annual Salary").

(b)   In addition to the Gross Annual Salary, I shall be entitled to receive the
additional compensation, if any, specified in Exhibit A, Item 3(b) ("Additional 
Compensation").

6.    DISABILITY. If I am is unable to fulfill the duties of my position by 
      ---------- 
reason of any illness, incapacity or disability, my salary shall be payable for 
only 90 days following the onset of such illness, incapacity or disability, 
provided, however, that if I (i) have applied for insurance benefits under the 
Company's long-term disability policy during said 90 day period, and (ii) have 
not yet begun to receive payments under said policy during said 90 day period, 
then my salary shall continue to be payable for up to 180 days following the 
onset of such illness, incapacity or disability until I begin to receive such 
payments. During the foregoing 90 day period (or 180 day period, if applicable),
my salary, to the extent not covered by the Company's short-term disability 
benefits, shall be paid through the use of my sick leave, if any, accumulated 
prior to January 1, 1994, but if such sick leave is or becomes exhausted, my 
salary shall nevertheless be paid for the 90 day period (or 180 day period, if 
applicable). If I shall return to full employment and full discharge of my 
duties during the term of this Agreement, full compensation shall be 
prospectively reinstated for any remaining term of this Agreement.

7.    TERMINATION AND SEVERANCE.
      -------------------------

(a)   Subject to Section 7(f) regarding a Change of Control, this Agreement may 
be terminated by either party without cause on six (6) months written notice to 
the other party. Subject to Section 7(f) regarding a Change of Control, this 
Agreement may be terminated by the Company immediately for cause by written 
notice to me. For purposes of this Section 7, cause for termination shall exist 
in the event of my dishonesty, chronic absenteeism, conviction of a felony, 
conviction of a misdemeanor involving moral turpitude, or material breach of 
this Agreement.

(b)   To the maximum extent permitted by law, I hereby expressly authorize the 
Company in advance upon my termination to deduct from my final paycheck(s) and 
from my paid time off (PTO) check all amounts I owe the Company (including but 
not limited to repayment of advances, loans or any other obligations).

(c)   Upon termination of employment, I will execute and comply with the 
Employee Termination Certificate attached hereto as Exhibit C, and deliver to 
the Company all notes, data, tapes, lists, reference materials, sketches, 
drawings, memoranda, records and other documents which are in my possession or 
control belonging to the Company or relating to its business.

(d)   Termination of this Agreement will not relieve me from my obligations 
under Sections 1(b), 2 and 3 of this Agreement, which, by their respective
terms, continue beyond the termination of this Agreement.

(e)   In the event of my death, this Agreement will terminate and all accrued 
and unpaid compensation and expenses, less all amounts I owe the Company 
(including but not limited to repayment of advances, loans or any other 
obligations), will be payable to my estate.

(f)   Notwithstanding any other provision of this Agreement to the contrary, at 
any time during the twelve-month period following a Change of Control (as 
hereinafter defined), (i) if the Company, with or without cause, terminates my 
employment or gives me notice of termination, or (ii) if I terminate my 
employment or give notice of termination by reason of a material breach by the 
Company of the terms of


                                      -3-
<PAGE>
 
this Agreement (including but not limited to the terms set forth on Exhibit A 
hereto), then I shall receive, in addition to any other compensation provided 
for in this Agreement, a lump-sum severance payment in an amount equal to the 
Gross Annual Salary, less any income, excise, employment or other tax 
withholdings which the Company is required by law to deduct therefrom.

(g)     For purposes of this Agreement, a Change in Control shall mean the 
satisfaction of the conditions set forth in any one of the following paragraphs:

        (i)   any person (as defined in Section 3(a)(9) of the Securities 
Exchange Act of 1934, as amended (the "Exchange Act") as modified and used in 
Sections 13(d) and 14(d) thereof, except that neither (A) the Company or any of 
                                  ------  
its subsidiaries, (B) a trustee or other fiduciary holding securities under an 
employee benefit plan of the Company or any of its subsidiaries, (C) an 
underwriter temporarily holding securities pursuant to an offering of such 
securities, nor (D) a corporation owned, directly or indirectly, by the 
stockholders of the Company in substantially the same proportions as their 
ownership of stock of the Company shall be included in such term) (a "Person") 
is or becomes the "beneficial owner" (as defined in Rule 13d-3 under the 
Exchange Act), directly or indirectly, of securities of the Company (not 
including in the securities beneficially owned by such Person any securities 
acquired directly from the Company or its affiliates) representing 25% or more
of the combined voting power of the Company's then outstanding securities; or

        (ii)   during any period of up to two consecutive years (not including 
any period prior to the execution of this Agreement), individuals who at the 
beginning of such period constitute the Board of Directors of the Company (the 
"Board") and any new director (other than a director designated by a Person who
has entered into an agreement with the Company to effect a transaction described
in clause (i), (iii) or (iv) of this paragraph) whose election by the Board or 
nomination for election by the Company's stockholders was approved by a vote of 
at least two thirds (2/3) of the directors then still in office who either were 
directors at the beginning of the period or whose election or nomination for 
election was previously so approved, cease for any reason to constitute a 
majority thereof; or

        (iii)  the shareholders of the Company approve a merger or consolidation
of the Company with any other corporation, other than (A) a merger or 
consolidation which would result in the voting securities of the Company 
outstanding immediately prior thereto continuing to represent (either by 
remaining outstanding or by being converted into voting securities of the 
surviving entity), in combination with the ownership of any trustee or other 
fiduciary holding securities under an employee benefit plan of the Company, at 
least 75% of the combined voting power of the voting securities of the Company 
or such surviving entity outstanding immediately after such merger or 
consolidation, or (B) a merger or consolidation effected to implement a 
recapitalization of the Company (or similar transaction) in which no Person 
acquires more than 50% of the combined voting power of the Company's then 
outstanding securities; or

        (iv)   the shareholders of the Company approve a plan of complete 
liquidation of the Company or an agreement for the sale or disposition by the 
Company of all or substantially all the Company's assets.

8.      NOTICE.
        ------

(a)     Any notice to be given to me under this Agreement shall be in writing 
and delivered by (i) registered or certified mail, return receipt requested; 
(ii) express courier; or (iii) hand-delivery, at an address specified for me in 
this Agreement or in any Exhibit hereto or at such other address of which 
written notice has been given to the Company by me by any of the foregoing 
means.

(b)     Any notice to be given to the Company under this Agreement shall be 
in writing and delivered by any of the means specified in subsection (a) above, 
to the President, with a copy to the Senior Vice





                                      -4-
<PAGE>
 

President, General Counsel & Secretary, GRC International, Inc., 1900 Gallows 
Road, Vienna, Virginia 22182.

9.   DISPUTES.
     --------

(a)  This Agreement has been executed in and shall be governed by the laws of 
the Commonwealth of Virginia.

(b)  Any controversy or claim arising out of or relating to Employee's 
employment or this Agreement shall be resolved in the courts of Fairfax County, 
Virginia, and Employee hereby submits to the jurisdiction of such courts, and 
agrees to accept service of process from such courts.

(c)  I understand and agree that the Company will suffer irreparable harm if I
breach any of my obligations under this agreement and that monetary damages may
be inadequate to compensate for such breach. Accordingly, in the event of a
breach or threatened breach by me, the Company, in addition to and not in
limitation of any other rights, remedies or damages available to it at
law or in equity or otherwise, shall be entitled to a injunctive relief
preventing any such breach by myself or by my partners, agents, representatives,
servants, employers, employees and/or any and all persons directly or indirectly
acting for or with me.

10.  ASSIGNMENT.  My services are unique and personal.  Accordingly, I may not 
     ----------
assign any rights or delegate any duties or obligations under this Agreement.  
The rights and obligations of the Company under this Agreement shall inure to 
the benefit of and shall be binding upon the successors and assigns of the 
Company.

11.  ENTIRE AGREEMENT.  This agreement, together with all documents attached to 
     ----------------
this agreement or specifically referred to in it, contains the entire agreement 
and understandings by and between the Company and me with respect to the 
covenants described in this agreement, and any representation, promise, 
agreement or understanding, written or oral, not contained in this agreement 
shall be of no force or effect.  No change or modification of this agreement 
shall be valid of binding unless the change or modification is in writing and 
signed by the parties to this agreement.  Any representation contrary to this 
agreement, express or implied, written or oral, is hereby disclaimed.  Nothing 
in this agreement shall obligate the Company to employ me for any length of 
time.  No waiver of any provision of this agreement shall be valid unless it is 
in writing and signed by the party against whom such waiver is sought to be 
enforced, and no waiver of any provision shall be deemed a waiver of any other 
provision or a waiver of the same provision at any other time.  This agreement 
supersedes all previous agreements between the Company and me.

12.  SEVERABILITY. Any provision of this agreement which may be determined to be
    ------------
unenforceable, invalid or illegal shall be deemed stricken from this agreement
and all remaining provisions shall continue in full force and effect.

13.  REASONABLENESS OF RESTRICTIONS.  I have carefully read and considered the 
     ------------------------------
provisions of this agreement and, having done so, agree that the restrictions 
set forth in this agreement are fair and reasonable and are reasonably required 
for the Company's protection.  This agreement shall be construed fairly as to 
all parties and not in favor of or against any party, regardless of which party 
prepared this agreement.  In the event that, notwithstanding the foregoing, any 
part of this agreement shall be held to be invalid or unenforceable, the 
remaining parts of the agreement shall nevertheless continue to be valid and 
enforceable as though the invalid or unenforceable parts had not been included 
in the agreement.  If any provision is held invalid or unenforceable with 
respect to particular circumstances, it shall nevertheless remain in full force 
and effect in all other circumstances.


                                      -5-

<PAGE>
 
IN WITNESS WHEREOF, the parties have executed this agreement as of the date 
first set forth above.


ATTEST:                                    GRC INTERNATIONAL, INC.
                                       
/s/ T.E. McCabe                            By: /s/ Jim Roth
--------------------------------               ---------------------------------
Thomas E. McCabe                               Jim Roth
Sr. Vice President, General                    President & Chief Executive
Counsel & Secretary                            Officer
                                       
                                       
                                       
WITNESS:                                   EMPLOYEE:
                                       
(SIGNATURE APPEARS HERE)                   /s/ Ronald B. Alexander
--------------------------------           -------------------------------------
                                           (Signature)
                                       
                                           /s/ Ronald B. Alexander
                                           -------------------------------------
                                           (Please print name)

APPROVED AND RATIFIED BY THE COMPENSATION COMMITTEE OF THE BOARD OF DIRECTORS 
OF GRC INTERNATIONAL, INC.


By: /s/ Leslie  B. Disharoon
   ---------------------------------------
   Leslie B. Disharoon, Committee Chairman




                                      -6-
<PAGE>
 
                                                                       EXHIBIT A
                                                                       ---------

                             DETAILS OF EMPLOYMENT
                             ---------------------

EMPLOYEE:  Ronald B. Alexander

ITEM 1(a) Position:  Senior Vice President, Treasurer & Chief Financial Officer

ITEM 1(b) Place of Employment: 1900 Gallows Road, Vienna, Virginia 22182

ITEM 2    Effective Date of Employment Agreement:  April 29, 1996

          Effective Date of this Exhibit:  April 29, 1996
 
ITEM 3(a) Gross Annual Salary:  One hundred sixty thousand dollars and no/100
                                ($160,000.00)
ITEM 3(b) Additional Compensation (if any): One-time bonus of forty thousands 
                                dollars ($40,000) payable October 29, 1996. 
                                Additional compensation (if any) to be 
                                determined annually by the President and CEO 
                                of GRC International, Inc.

ITEM 4 Notice to Employee:

       1900 Gallows Road                      3122 Miller Heights Road
     ------------------------------         ------------------------------
                                       and/
       Vienna, Virginia 22182           or    Oakton, Virginia 22124
     ------------------------------         ------------------------------

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


EMPLOYEE:                                     GRC INTERNATIONAL, INC.

[SIGNATURE APPEARS HERE]                      By: /s/ Jim Roth
                                                 -----------------------------
                                                 Jim Roth
                                                 President & Chief Executive 
                                                 Officer


APPROVED AND RATIFIED BY THE COMPENSATION COMMITTEE OF THE BOARD OF DIRECTORS OF
GRC INTERNATIONAL, INC.

By: /s/ Leslie B. Disharoor
   ---------------------------------------------
   Leslie B. Disharoor, Committee Chairman

                                      -7-
<PAGE>
 
                                                            EXHIBIT B
                                                            ---------

                       SCHEDULE OF INTELLECTUAL PROPERTY
                       ---------------------------------

I developed or conceived prior to employment with the Company, and consider 
proprietary to me, the following intellectual Property, as that term is defined 
in the Employment Agreement to which this Exhibit is attached:







                                                   EMPLOYEE
                                                          
                                                    /s/ Ronald B. Alexander
                                                   ---------------------------
                                                   (signature)

                                                    /s/ Ronald B. Alexander
                                                   ---------------------------
                                                   (Please print name)

                                                    April 29, 1996
                                                   ---------------------------
                                                   (Date)

                                      -8-
<PAGE>
 
                                                               EXHIBIT C
                                                               ---------
                             TERMINATION STATEMENT
                             ---------------------

                 (to be signed upon termination of employment)

1.     I,_____________________________________(employee's name), am cognizant of
my legal obligations, as stated in a certain EMPLOYMENT AGREEMENT dated ________
_________________________ between myself and GRC International, Inc. (together 
with its subsidiaries, the "Company"), and I hereby specifically reaffirm all of
the terms stated in that agreement.

2.     I hereby certify that all materials related directly or indirectly to my
employment with the Company have been returned to the Company. I further certify
that no computer listings, programs, object codes, source codes, product
development guides, flowcharts, test equipment, drawings, blueprints or other
materials owned by the Company or provided to or used by me in connection with
any employment at the Company, whether in machine-readable form or otherwise,
have been retained by me or given to any other third person or entity in
anticipation of my employment termination or for any other reason, and I also
certify that none of those materials will be removed from the Company's premises
by me.

3.     I also certify that I have returned all company identification and credit
cards issued to me and all keys to Company and/or customer property that have
been in my possession.

4.     I am not aware of any action or situation involving any violation of the 
Company's Corporate Standards of Conduct by any employee, director, consultant 
or representative of the Company, except as follows:


5. My forwarding addresses are as follows:

               HOME ADDRESS                             BUSINESS ADDRESS

       ___________________________                ___________________________

       ___________________________                ___________________________

       ___________________________                ___________________________

       ___________________________                ___________________________


                                          EMPLOYEE:

                                          ________________________________
                                          (Signature)

                                          ________________________________
                                          (Please print name)

                                          ________________________________
                                          (Date)


                                      -9-