Two U.S. Navy F14 fighters from the aircraft carrier Eisenhower had a head-on encounter with two Libyan warplanes over the Gulf of Sidra on Monday, the Pentagon announced last night.

The incident, which did not involve weapons, was reported as senior administration officials revealed that the United States is urging France to provide immediate air support for the government of Chad to counter intensifying bombing raids by Libya in the northern part of the country.

Chad yesterday denied Libyan reports that President Hissene Habre was among those killed in the Libyan bombing of Faya Largeau, a strategic oasis 500 miles north of the capital, Ndjamena. Foreign Minister Idriss Miskine described the attacks as "virtual genocide."

The nuclear-powered Eisenhower is part of a U.S. carrier battle group operating in the central Mediterranean off Libya. The Pentagon spokesman said of Monday's incident: "The Libyan MiG23s turned to avoid collision, then descended and headed for shore."

The United States and France both announced on Monday that they were sending antiaircraft missiles to Chad, but the French fell short of meeting a request from Habre for air support against Libyan-backed rebels.

The officials said that if the French did agree to provide aerial cover for the Chadian Army, the United States would consider helping with logistical support, possibly refueling. It was not clear at this stage, however, what form such American assistance might take.

Western diplomats in Chad were quoted as saying that the rebels, led by former president Goukouni Oueddei, hoped the Libyan air raids would help them take Faya Largeau before the American and French antiaircraft weapons could be deployed.

State Department spokesman Alan Romberg said that the U.S. weapons--shoulder-fired, heat-seeking Redeye missiles--were already en route to Chad "and should arrive shortly." A later statement said that a "small team of trainers" was going to Ndjamena to instruct the Chadian Army in their use.

"We expect that they will remain in Ndjamena, which is several hundred miles away from the fighting," the statement said. "They will be there for a very brief time, no more than a few days." Pentagon officials said they were looking into the possibility that French personnel already in the country might help instruct the Chadians on the Redeyes.

Rebel forces in Chad claimed Tuesday that they had retaken Faya Largeau. The rebels' Bardai Radio, monitored by the British Broadcasting Corp., said the town was recaptured after a 72-hour siege, Reuter reported.

[The Chadian government Tuesday night asked the U.N. Security Council for an urgent meeting. The Foreign Ministry issued a statement saying it wanted the council to take up "Libya's intensified aggression."]