**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 havereviewed this quarterly report on Form 10-Q of SI International, Inc.; 

 

2.  Based on my knowledge, this quarterlyreport does not contain any untrue statement of a material fact or omit tostate a material fact necessary to make the statements made, in light of thecircumstances under which such statements were made, not misleading withrespect to the period covered by this quarterly report; 

 

3.  Based on my knowledge, the financialstatements, and other financial information included in this quarterly report,fairly present in all material respects the financial condition, results ofoperations and cash flows of the registrant as of, and for, the fiscal quartersand fiscal years presented in this quarterly report; 

 

4.  The registrant’s other certifyingofficers and I are responsible for establishing and maintaining disclosurecontrols and procedures (as defined in Exchange Act Rules 13a-14 and 15d-14)for the registrant and we have: 

 

a)  Designed such disclosure controls andprocedures 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 fiscal period in which this quarterlyreport is being prepared; 

 

b)  Evaluated the effectiveness of theregistrant’s disclosure controls and procedures as of a date within 90 daysprior to the filing date of this quarterly report (the “Evaluation Date”); and 

 

c)  Presented in this quarterly report ourconclusions about the effectiveness of the disclosure controls and proceduresbased on our evaluation as of the Evaluation Date; 

 

5.  The registrant’s other certifyingofficers and I have disclosed, based on our most recent evaluation, to theregistrant’s auditors and the audit committee of the registrant’s board ofdirectors (or persons performing the equivalent function):

 

a)  All significant deficiencies in thedesign or operation of internal controls which could adversely affect theregistrant’s ability to record, process, summarize and report financial dataand have identified for the registrant’s auditors any material weaknesses ininternal controls; and 

 

b)  Any fraud, whether or not material,that involves management or other employees who have a significant role in theregistrant’s internal controls; and 

 

6.  The registrant’s other certifying officersand I have indicated in this quarterly report whether or not there weresignificant changes in internal controls or in other factors that couldsignificantly affect internal controls subsequent to the date of our mostrecent evaluation, including any corrective actions with regard to significantdeficiencies and material weaknesses. 

 

November      ,2003

 

 
|   |   | By:    |                                                                  |
|--------|--------|--------|-----------------------------------------------------------------------|
|   |   |   | 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.  I have reviewed thisquarterly report on Form 10-Q of SI International, Inc.; 

 

2.  Based on my knowledge, this quarterlyreport does not contain any untrue statement of a material fact or omit tostate a material fact necessary to make the statements made, in light of thecircumstances under which such statements were made, not misleading withrespect to the period covered by this quarterly report; 

 

3.  Based on my knowledge, the financialstatements, and other financial information included in this quarterly report,fairly present in all material respects the financial condition, results of operationsand cash flows of the registrant as of, and for, the fiscal quarters and fiscalyears presented in this quarterly report; 

 

4.  The registrant’s other certifyingofficers and I are responsible for establishing and maintaining disclosurecontrols and procedures (as defined in Exchange Act Rules 13a-14 and 15d-14)for the registrant and we have: 

 

a)  Designed such disclosure controls andprocedures 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 fiscal period in which this quarterlyreport is being prepared; 

 

b)  Evaluated the effectiveness of theregistrant’s disclosure controls and procedures as of a date within 90 daysprior to the filing date of this quarterly report (the “Evaluation Date”); and 

 

c)  Presented in this quarterly report ourconclusions about the effectiveness of the disclosure controls and proceduresbased on our evaluation as of the Evaluation Date; 

 

5.  The registrant’s other certifyingofficers and I have disclosed, based on our most recent evaluation, to theregistrant’s auditors and the audit committee of the registrant’s board ofdirectors (or persons performing the equivalent function):

 

a)  All significant deficiencies in thedesign or operation of internal controls which could adversely affect theregistrant’s ability to record, process, summarize and report financial dataand have identified for the registrant’s auditors any material weaknesses ininternal controls; and 

 

b)  Any fraud, whether or not material,that involves management or other employees who have a significant role in theregistrant’s internal controls; and 

 

6.  The registrant’s other certifyingofficers and I have indicated in this quarterly report whether or not therewere significant changes in internal controls or in other factors that couldsignificantly affect internal controls subsequent to the date of our mostrecent evaluation, including any corrective actions with regard to significantdeficiencies and material weaknesses. 

 

November     ,2003
|   |   | By:    |                                                                               |
|--------|--------|--------|------------------------------------------------------------------------------------|
|   |   |   |                                                                               |
|   |   |   | Thomas E. Dunn**Executive Vice President,  Chief Financial Officer and Treasurer** |

 

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