**Exhibit 31.1**

 

**CERTIFICATION OF CHIEF EXECUTIVE OFFICERPURSUANT TO RULE 13a-14(a) AS ADOPTED PURSUANT TO SECTION 302 OF THE SARBANES-OXLEY ACT OF 2002**

 

I,Ray J. Oleson, certifythat: 

 

1.  I have reviewed this quarterly report onForm 10-Q of SI International, Inc.; 

 

2.  Basedon my knowledge, this report does not contain any untrue statement of amaterial fact or omit to state a material fact necessary to make the statementsmade, in light of the circumstances under which such statements were made, notmisleading with respect to the period covered by this report; 

 

3.  Basedon my knowledge, the financial statements, and other financial informationincluded in this report, fairly present in all material respects the financialcondition, results of operations and cash flows of the registrant as of, andfor, the periods presented in this report; 

 

4.  Theregistrant’s other certifying officer(s) and I are responsible for establishingand maintaining disclosure controls and procedures (as defined in Exchange ActRules 13a-15(e) and 15d-15(e)) for the registrant and have: 

 

a)  Designed such disclosure controls and procedures, orcaused such disclosure controls and procedures to be designed under oursupervision, to ensure that material information relating to the registrant,including its consolidated subsidiaries, is made known to us by others withinthose entities, particularly during the period in which this report is beingprepared;

 

b)  [Omitted pursuant to “Management’s Reports on InternalControl Over Financial Reporting and Certification of Disclosure in ExchangeAct Periodic Reports,” SEC Release No. 33-8238 (June 5, 2003)];

 

c)  Evaluated the effectivenessof the registrant’s disclosure controls and procedures and presented in thisreport our conclusions about the effectiveness of the disclosure controls andprocedures, as of the end of the period covered by this report based on suchevaluation; and 

 

d)  Disclosed in this report any change in the registrant’sinternal control over financial reporting that occurred during the registrant’smost recent fiscal quarter that has materially affected, or is reasonablylikely to materially affect, the registrant’s internal control over financialreporting; and 

 

5.  Theregistrant’s other certifying officer(s) and I have disclosed, based on ourmost recent evaluation of internal control over financial reporting, to theregistrant’s auditors and the audit committee of the registrant’s board ofdirectors (or persons performing the equivalent functions):

 

a)  All significant deficiencies and material weaknesses inthe design or operation of internal control over financial reporting which arereasonably likely to adversely affect the registrant’s ability to record,process, summarize and report financial information; and 

 

b)  Any fraud, whether or notmaterial, that involves management or other employees who have a significantrole in the registrant’s internal control over financial reporting. 

 
| May  11th, 2004 |   |                                               |   |
|-----------------|--------|----------------------------------------------------|--------|
|            |   |                                               |   |
|            | By:    | /s/ Ray J. Oleson                                  |   |
|            |   | Ray  J. Oleson                                     |
|            |   | Chairman of the Board and  Chief Executive Officer |

 

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**CERTIFICATION OF CHIEF FINANCIAL OFFICERPURSUANT TO RULE 13a-14(a) AS ADOPTED PURSUANT TO SECTION 302 OF THE SARBANES-OXLEY ACT OF 2002**

 

I,Thomas E. Dunn, certify that: 

 

1.  Ihave reviewed this quarterly report on Form 10-Q of SI International, Inc.; 

 

2.  Basedon my knowledge, this report does not contain any untrue statement of amaterial fact or omit to state a material fact necessary to make the statementsmade, in light of the circumstances under which such statements were made, notmisleading with respect to the period covered by this report; 

 

3.  Basedon my knowledge, the financial statements, and other financial informationincluded in this report, fairly present in all material respects the financialcondition, results of operations and cash flows of the registrant as of, andfor, the periods presented in this report; 

 

4.  Theregistrant’s other certifying officer(s) and I are responsible for establishingand maintaining disclosure controls and procedures (as defined in Exchange ActRules 13a-15(e) and 15d-15(e)) for the registrant and have: 

 

a)  Designed such disclosure controls and procedures, orcaused such disclosure controls and procedures to be designed under oursupervision, to ensure that material information relating to the registrant,including its consolidated subsidiaries, is made known to us by others withinthose entities, particularly during the period in which this report is beingprepared; 

 

b)  [Omitted pursuant to “Management’s Reports on InternalControl Over Financial Reporting and Certification of Disclosure in ExchangeAct Periodic Reports,” SEC Release No. 33-8238 (June 5, 2003)];

 

c)  Evaluated the effectiveness of the registrant’sdisclosure controls and procedures and presented in this report our conclusionsabout the effectiveness of the disclosure controls and procedures, as of theend of the period covered by this report based on such evaluation; and 

 

d)  Disclosed in this report any change in the registrant’s internalcontrol over financial reporting that occurred during the registrant’s mostrecent fiscal quarter that has materially affected, or is reasonably likely tomaterially affect, the registrant’s internal control over financial reporting;and

 

5.  Theregistrant’s other certifying officer(s) and I have disclosed, based on ourmost recent evaluation of internal control over financial reporting, to theregistrant’s auditors and the audit committee of the registrant’s board ofdirectors (or persons performing the equivalent functions):

 

a)  All significant deficiencies and material weaknesses inthe design or operation of internal control over financial reporting which arereasonably likely to adversely affect the registrant’s ability to record,process, summarize and report financial information; and 

 

b)  Any fraud, whether or not material, that involvesmanagement or other employees who have a significant role in the registrant’sinternal control over financial reporting. 

 
| May  11th, 2004 |   |                                                             |
|-----------------|--------|------------------------------------------------------------------|
|            |   |                                                             |
|            | By:    | /s/ Thomas E. Dunn                                               |   |
|            |   | Thomas  E. Dunn                                                  |
|            |   | Executive Vice President,  Chief Financial Officer and Treasurer |

 

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