Citing engineering problems and a lack of testing, a congressional agency is recommending a delay in the Air Force's cherished F-22 fighter program, a move the Air Force says would add billions of dollars in costs.

In an unpublished report, the General Accounting Office, an investigative arm of Congress, said the Pentagon should delay a decision to spend $595 million on the first two production planes until late 1999. The report's basic recommendation was obtained Wednesday by The Associated Press.The Air Force insisted Wednesday it was ready to approve production in December 1998 and that a delay would add billions to the cost.

The $62 billion F-22 is the premier Air Force weapons program and is expected to become one of the Pentagon's biggest single investments in the coming years. Designed to replace the F-15, it uses stealth or radar-evading technology and is intended primarily to combat enemy fighter aircraft.