* SI International, a Reston government contractor, earned $2.9 million (33 cents a share) in the three months ended Sept. 25, compared with a $2 million (23 cents) profit for the same period of the previous year. The company's third-quarter revenue rose to $72.9 million from $42.1 million. Shares of SI, which reported its results after markets closed, fell $1.04 yesterday to close at $25.64.

* Science Applications International, a San Diego engineering company, acquired Presearch, a Fairfax naval systems engineering and data mining company. Terms were not disclosed. Upon completion of the acquisition, all 150 Presearch employees will transition into SAIC's research and intelligence group. Presearch's clients include the military, intelligence agencies and customers in the energy, pharmaceutical and banking industries. Privately owned Presearch was founded in 1963 by Leonard P. Gollobin, its chief executive.

* BAE Systems North America, a Rockville defense contractor, completed its acquisition of DigitalNet Holdings for $30.25 per share, or about $600 million in cash plus the assumption of DigitalNet's debt of $93.25 million. DigitalNet, a managed network services provider, will become part of BAE Systems' information technology unit.

* Intersections, a Chantilly credit management services company, earned $3.5 million (19 cents a share) on $38.6 million in revenue during its third quarter, down from a profit of $9.5 million (65 cents) on $38 million in revenue in the corresponding quarter a year ago. For the nine months ended Sept. 30, the company earned $8.6 million (52 cents) on $117 million in revenue, down from $16.9 million ($1.18) on $110.8 million in revenue during the same period last year. Shares closed down 28 cents at $12.75.

* AceComm, a Gaithersburg communications company, lost $383,000 (3 cents a share) on $4.7 million in revenue during its first fiscal quarter ended Sept. 30, compared with a loss of $980,000 (10 cents) on $2.5 million in revenue during the corresponding quarter a year ago. Shares closed down 11 cents at $1.75.

* Official Payments, a Stamford, Conn., subsidiary of Tier Technologies of Reston, signed a two-year contract extension with the Commonwealth of Virginia Department of Taxation to provide electronic payment services that allow people and businesses in the state to pay taxes with a credit card via the Internet or telephone.

Compiled from reports by Washington Post staff writers.