The Air Force, under the gun to challenge General Dynamics Corp.'s monopoly on building light tactical fighters, has given up hope of meeting the July 1 deadline set by Congress for a "fly-off" of competing aircraft, Pentagon officials said yesterday.

Officials said the competition -- one of the hottest in the aerospace industry -- is expected to stretch into October. Congress mandated a speedy contest after Northrop Corp. offered last April to sell its F20 Tigershark for what it said was a substantially lower price than the $18 million charged by General Dynamics for its F16 Falcon.

General Dynamics, which has been at the center of some military procurement scandals, agreed two months later to sell the Air Force a stripped-down version of the F16 for $2 million less than Northrop's $12 million F20.

Congressional conferees, hoping that competition might drive down the cost of Air Force fighters, called for an "expedited" contest between the F16 and the F20 in the current fiscal year, which ends Sept. 30. Since both aircraft are well known to the Air Force, the lawmakers expected the contest to be complete early enough to permit "prudent expenditure" of $200 million appropriated this fiscal year.

Col. Richard Bedarf, chief of the Air Force's tactical fighter division, said that, in order to thoroughly analyze each plane's cost and performance, the competition will require more time than Congress allotted.

"We have to do this right so that we can defend the decision," he said.

So far, the contest has centered on General Dynamics and Northrop, but four other major contractors have expressed interest, including McDonnell Douglas Corp., manufacturer of the F4.

Northrop wants an early decision because it is spending $18 million a month on the F20, which it developed for overseas sale but has yet to sell. Foreign customers often balk at weapons not in the U.S. inventory.

"The bureaucracy doesn't like this [contest] because it's something new," a source close to Northrop said. "They're slow-rolling this thing in the hope it will go away."

A General Dynamics official said Northrop is trying to obtain a "rubber stamp for the F20" by pushing the Air Force faster than it wants to go. "The Air Force is saying, if you want to have a legitimate competition, it can't go that fast," he said.