The United States and France have decided to send antiaircraft weapons to Chad after three days of Libyan air raids in the north of the Central African country, Washington and Paris announced yesterday in a move underlining their growing concern about the extent of Libyan support for antigovernment insurgents.

The United States will send an unspecified quantity of shoulder-fired Redeye guided missiles to the Chadian Army, according to senior administration officials who expanded on a State Department announcement specifying "antiaircraft weapons."

The decision follows weekend consultations led by Secretary of State George P. Shultz and a strongly worded State Department condemnation of Libyan "aggression."

The United States previously had been content to let France take the lead in backing the government of Chadian President Hissene Habre, and until yesterday had refrained from committing weapons to the fight against the Libyan-backed insurgents.

Yesterday's announcement, however, came concurrently with announcement in Paris of the French move, which, according to Washington Post correspondent Michael Dobbs, fell short of meeting a request by the government in Ndjamena for air support against the rebels.

The U.S. administration was in close contact with the French government during the weekend as the situation developed, officials said.

The State Department announcement said the antiaircraft weapons will give Chadian government forces "a better opportunity to defend themselves against continuing attacks by Libyan warplanes."

The U.S. move follows last week's authorization by President Reagan of an "urgent" $10 million airlift of military supplies to Chad. The State Department described that shipment as "nonlethal" equipment such as food, clothing, radios and some vehicles, but congressional sources said yesterday it also included rifles, machine guns and ammunition.

The Pentagon would not confirm reports that a U.S. aircraft carrier battle group was on standby off Libya in the event of continued air raids in Chad. A spokesman would say only that the Eisenhower and the Coral Sea were both "operating in the central Mediterranean."

Habre appealed for French and U.S. aid after Libyan MiG fighter-bombers reportedly made at least three bombing runs over the northern oasis town of Faya Largeau on Sunday.

"Habre has nothing in terms of antiaircraft defense and his people are being pounded on a continual basis by the Libyans," one administration official said yesterday.

The official said that the weapons would be sent immediately and that their delivery would not require any long-term U.S. involvement. "We may have to have a couple of people to unpack them and then show the Chadians how to use them," he said.

The Redeye is a portable, shoulder-fired guided missile that employs infra-red homing to destroy low-flying aircraft.

Events in Chad will figure prominently in talks this week in Washington with the visiting president of Zaire, Mobutu Sese Seko, U.S. officials indicated yesterday. Mobutu, who arrives today, has reportedly sent some 2,000 paratroopers and half a dozen combat aircraft to back Habre.

Washington Post correspondent Michael Dobbs added from Paris:

Chad's request for French air support was made in a letter from President Habre to President Francois Mitterrand that was delivered to the French Embassy in the Chadian capital Sunday.

In addition to seeking support from France and the United States, Habre appealed for backing from several friendly African countries, including Zaire, Egypt, Morocco and Sudan.

Libya has denied conducting air raids on Faya Largeau but has not hidden its sympathies for the rebels led by former president Goukouni Oueddei. Goukouni's 4,000-man army is known to have relied on Libyan equipment and logistical support during its offensive in June and July, and the Habre government claims to have captured several Libyan soldiers.

A massive airlift of French military equipment appeared to mark a turning point in the war last month after a series of defeats for Habre. The equipment, which included vehicles, light artillery pieces and other weapons, was provided under a military cooperation treaty signed in 1976 by France and its former colony.

Aware of a long history of French entanglements in the landlocked African state, Mitterrand insisted that the treaty did not provide for the dispatch of any French soldiers to Chad. He also refused to send Jaguar tactical support aircraft stationed at a French base in the West African state of Gabon.

French journalists in Chad have, however, reported that several dozen French civilian technicians have been assisting Habre's troops in using the military equipment.

A spokesman for the French Foreign Ministry said yesterday that sending antiaircraft weapons did not mean a change in the French position, but merely "an adapting of logistical support" to battlefield conditions.