Navy fighter jets from the fleet of U.S. warships concentrated in the Mediterranean north of Libya made their first crossing yesterday over Muammar Qaddafi's "line of death" and flew deep into the Gulf of Sidra, administration officials said yesterday.

Libyan forces did not confront the Navy jets, sources said. The fighters included F14 Tomcats, armed with long-range and short-range air-to-air missiles considered superior to anything in the Libyan arsenal.

Pentagon spokesman Robert B. Sims refused to confirm or deny the reports last night. He noted that the United States formally filed a notice of its intent to conduct Navy flight operations off Libya for 10 days.

Sims said the Pentagon will not announce any crossings of the so-called line of death. The administration appears to be trying to pull the spotlight off the naval buildup in the Gulf of Sidra region.

The penetration was a limited one, sources said, to be followed later with crossings by additional aircraft and warships at 32 minutes and 30 seconds north latitude where Qaddafi has threatened to attack. That line takes in most of the elbow-shaped gulf. The United States and other maritime nations recognize Libyan territorial waters extending only 12 miles from shore.

Defense Secretary Caspar W. Weinberger said on NBC News' "Meet The Press" yesterday that U.S. Navy ships had operated in the Gulf of Sidra many times and any further operations in the gulf would be considered routine.

However, the administration made elaborate plans this time to penetrate deep into the gulf, sources said, including authorizing U.S. planes and ships to fire back if the Libyans attacked while they were in the Gulf of Sidra. It is highly unusual to mass three aircraft carriers and escorting warships off the gulf for one operation.

The carriers now in position off Libya are the USS America, USS Coral Sea and USS Saratoga. In all, they carry more than 240 planes and are escorted by 27 warships, including cruisers, frigates and destroyers.

Vice Admiral Frank B. Kelso II, Sixth Fleet commander, is directing the operations from his flagship, the USS Coronado. He is expected to order a few of the escorting warships, but not the carriers, to cross the 32.5-minute parallel within the next 10 days.

Once the United States reasserts its right to use the Gulf of Sidra up to 12 miles from the Libyan coast, officials said, the Navy will reduce its force off Libya to one carrier. The Saratoga and Coral Sea are scheduled to leave the Mediterranean shortly after the penetrations are completed, officials said.

While it could not be learned last night how many aircraft were involved in the first crossing, sources said it involved at least one flight of F14s. It was not clear whether aircraft other than F14s were involved in yesterday's action.

The standard tactic for the sort of penetration conducted yesterday, sources said, is to send two F14s out together, one serving as the leader and the second flying on its right wing. This was the type formation the Navy was flying when it shot down two Libyan planes in August 1981.

Some military officials believe the administration's tactics are designed to provoke Qaddafi into attacking, which would then give the United States grounds for retaliation. U.S. officials deny this, however, and said they are asserting the right of navigation in the Gulf of Sidra.