The "Stealth" fighter has been put back under wraps after the Pentagon quashed a planned announcment that the Air Force has had the radar-evading jet since 1981, congressional and defense officials said.

"The decision is fairly obvious . . . . We decided not to do a briefing at this time," Pentagon spokesman Dan Howard told reporters on Tuesday, without elaboration.Other officials, who asked not to be identified, told Reuters that congressional leaders opposed the planned Air Force announcement, which they said had been backed by some supporters of Vice President George Bush.

Bush, involved in a close race with Democrat Michael Dukakis, has boasted of the U.S. defense buildup under President Reagan and has accused Dukakis of being soft on defense.

Democratic Sen. Sam Nunn of Georgia, chairman of the Senate Armed Services Committee, said he personally called Defense Secretary Frank Carlucci and complained when he found out that the Air Force planned the announcement.

Despite widely published reports, the Air Force has never acknowledged existence of a fighter which is virtually immune to radar detection.

Howard declined comment on reports that the plane - one of the Pentagon's top secret "black projects" - has been flying since 1981 and that 59 of them are based at an airfield in Nevada.

He also refused to confirm or deny a report in Tuesday's Washington Times that the fighter is a single-seat jet which flies at subsonic speeds and has a skin with sharp edges and points to render a confusing radar picture.

"Apparently, clearer heads prevailed here," one congressional official told Reuters.

"Members of the defense committees complained and the Air Force woke up and realized you don't simply announce this thing, even if everybody knows there is a Stealth," he said.