**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 reportdoes not contain any untrue statement of a material fact or omit to state amaterial 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 report;

 

3.  Based on my knowledge, the financialstatements, and other financial information included in this report, fairlypresent in all material respects the financial condition, results of operationsand cash flows of the registrant as of, and for, the periods presented in thisreport;

 

4.  The registrant’s other certifyingofficer(s) and I are responsible for establishing and maintaining disclosurecontrols and procedures (as defined in Exchange Act Rules 13a-15(e) and15d-15(e)) for the registrant and have:

 

a)  Designed such disclosure controls andprocedures, or caused such disclosure controls and procedures to be designedunder our supervision, 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’sReports on Internal Control Over Financial Reporting and Certification ofDisclosure in Exchange Act Periodic Reports,” SEC Release No. 33-8238(June 5, 2003)];

 

c)  Evaluatedthe effectiveness of the registrant’s disclosure controls and procedures andpresented in this report our conclusions about the effectiveness of thedisclosure controls and procedures, as of the end of the period covered by thisreport based on such evaluation; and

 

d)  Disclosed in this report any change inthe registrant’s internal control over financial reporting that occurred duringthe registrant’s most recent fiscal quarter that has materially affected, or isreasonably likely to materially affect, the registrant’s internal control overfinancial reporting; and

 

5.  The registrant’s other certifyingofficer(s) and I have disclosed, based on our most recent evaluation ofinternal control over financial reporting, to the registrant’s auditors and theaudit committee of the registrant’s board of directors (or persons performingthe equivalent functions):

 

a)  All significant deficiencies andmaterial weaknesses in the design or operation of internal control overfinancial reporting which are reasonably likely to adversely affect theregistrant’s ability to record, process, summarize and report financialinformation; and

 

b)  Any fraud,whether or not material, that involves management or other employees who have asignificant role in the registrant’s internal control over financial reporting.

 
|   | November  4, 2004          |   | SI  INTERNATIONAL, INC. |
|--------|----------------------------|--------|-------------------------|
|   |                       |
|   |                       |
|   | /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.  I have reviewed thisquarterly report on Form 10-Q of SI International, Inc.;

 

2.  Based on my knowledge, this reportdoes not contain any untrue statement of a material fact or omit to state amaterial fact necessary to make the statements made, in light of the circumstancesunder which such statements were made, not misleading with respect to theperiod covered by this report;

 

3.  Based on my knowledge, the financialstatements, and other financial information included in this report, fairlypresent in all material respects the financial condition, results of operationsand cash flows of the registrant as of, and for, the periods presented in thisreport;

 

4.  The registrant’s other certifyingofficer(s) and I are responsible for establishing and maintaining disclosure controlsand procedures (as defined in Exchange Act Rules 13a-15(e) and 15d-15(e)) forthe registrant and have:

 

a)  Designed such disclosure controls andprocedures, or caused such disclosure controls and procedures to be designedunder our supervision, to ensure that material information relating to theregistrant, including its consolidated subsidiaries, is made known to us byothers within those entities, particularly during the period in which thisreport is being prepared;

 

b)  [Omitted pursuant to “Management’sReports on Internal Control Over Financial Reporting and Certification ofDisclosure in Exchange Act Periodic Reports,” SEC Release No. 33-8238 (June 5,2003)];

 

c)  Evaluatedthe effectiveness of the registrant’s disclosure controls and procedures andpresented in this report our conclusions about the effectiveness of thedisclosure controls and procedures, as of the end of the period covered by thisreport based on such evaluation; and

 

d)  Disclosed in this report any change inthe registrant’s internal control over financial reporting that occurred duringthe registrant’s most recent fiscal quarter that has materially affected, or isreasonably likely to materially affect, the registrant’s internal control overfinancial reporting; and

 

5.  The registrant’s other certifyingofficer(s) and I have disclosed, based on our most recent evaluation ofinternal control over financial reporting, to the registrant’s auditors and theaudit committee of the registrant’s board of directors (or persons performingthe equivalent functions):

 

a)  All significant deficiencies andmaterial weaknesses in the design or operation of internal control overfinancial reporting which are reasonably likely to adversely affect theregistrant’s ability to record, process, summarize and report financialinformation; and

 

b)  Any fraud, whether or not material,that involves management or other employees who have a significant role in theregistrant’s internal control over financial reporting.

 
| November  4, 2004 |                                   | SI  INTERNATIONAL, INC. |
|-------------------|----------------------------------------|-------------------------|
|              |                                   |
|              |                                   |
|              | /s/ Thomas E. Dunn                     |                    |
|              | Thomas  E. Dunn                        |
|              | Executive  Vice President,             |
|              | Chief  Financial Officer and Treasurer |

 

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