BAE Systems North America, the Rockville-based division of a British defense services company, announced yesterday that it signed a definitive agreement to acquire a Washington-based defense contractor, Advanced Power Technologies Inc., for $27 million in cash.

The deal is subject to approval by the Department of Defense and other regulatory bodies; it is expected to close in about 45 days.

Advanced Power Technologies (APTI), a 17-year-old company, generated $26 million in revenue last year. . It specializes in gathering and processing intelligence, surveillance and reconnaissance information. It has been a subcontractor with BAE, and the deal will enable the companies to expand, officials at both companies said.

"We are very pleased and excited," said Leonard Lynch, vice president and chief financial officer of APTI. The firm employs 110 people, almost all of whom work out of its offices in the District, Maryland and Virginia. The company does not anticipate changes to its management or workforce as a result of the proposed acquisition, he said.

BAE, which employs 22,000 people in North America, is a London-based defense giant that designs and builds aircraft, destroyers and space-related vehicles. Its U.S.-based division specializes in electronic and information technology systems that are used in military command and control centers.

"[APTI's] particular line of work is very much within our specialty, and our long-term strategy is to grow," said Joan Ferguson, a spokeswoman for BAE. The company's interest in consolidation has been an ongoing process, driven more by the growth in complexity of information systems and less by the immediate need for homeland defense and military surveillance, she said.

APTI was founded as a subsidiary of Atlantic Richfield Co. In 1994, it was sold to Dallas-based E-Systems Inc., which was sold to Raytheon Co. in 1995. Then, through a management buyout in January 1998, APTI was spun off and it became a privately held company.