Jet fighters from two U.S. aircraft carriers operated north of Libya yesterday as Libyan leader Col. Muammar Qaddafi sent Soviet-made warplanes into the area, but there was no reported contact between the forces, administration officials said.

Several Libyan MiG23 and MiG25 fighters flew north of the Gulf of Sidra where the U.S. warplanes were operating as part of a naval exercise, the officials said. The Libyan jets approached within six miles but no attempt was made to intercept the American planes, they said.

"There was no evidence of hostile intent and no encounter," an administration official said.

Pentagon officials said U.S. F/A18 and F14 fighters, accompanied by E2C reconnaissance planes, conducted their exercises north of the gulf, a large body of water that cuts into the Libyan coastline. Qaddafi claims that the gulf and its airspace as Libyan territory.

The United States recognizes territorial waters as extending only 12 miles from the Libyan coast, and defense officials yesterday reaffirmed the right of American planes to enter the gulf. The U.S. Navy exercises centered around the carriers USS Coral Sea and USS Saratoga began at 7 p.m. Thursday Washington time and are intended as a show of American military resolve in the face of threats by Qaddafi to support attacks against "Zionist" and "imperialist" targets, officials said.

Declaring that U.S. warplanes will conduct operations in the Tripoli Flight Information Region (FIR), which extends more than 700 miles off the Libyan coast, the Pentagon said in a statement that "the Gulf of Sidra is in the Tripoli FIR."

"We see it as a routine exercise unless the Libyans get crazy, which they are capable of," said a senior Pentagon official. Administration officials said the exercise, which is expected to last a week, is intended in part to force the Libyans to remain on military alert, which requires a costly outlay of fuel and supplies.

Pentagon officials noted severe operational problems encountered by Libya's navy when Qaddafi sent his ships to sea earlier this month to disperse potential targets for U.S. forces that might have retaliated for the Dec. 27 attacks on the Rome and Vienna airports.

Libyan sailors were reportedly seasick while some of their ships were breaking down on the Mediterranean or dead in the water to save fuel. Libyan pilots ordered to keep their planes aloft at night to escape surprise attack were afraid of getting lost in the dark, Pentagon officials said.

"If this is a war of nerves," a U.S. official said of current exercises, "it's the Libyans who are getting nervous."