The United States yesterday signaled to France its determination to support the government of Chad against Libyan-backed rebels by sending two AWACS surveillance aircraft, accompanied by fighters, to monitor air attacks on a key loyalist stronghold in the central African country.

U.S. officials said they believe the French government is close to deciding whether to intervene in the growing civil war. Chadian President Hissene Habre appealed to Paris and Washington for further support against the rebels.

A U.S. official said he hoped that the dispatch of the AWACS would help convince Paris of Washington's determination to stand up to what the American government has called Libyan "aggression" and to encourage the French to do the same.

The State Department announced that the two AWACS, with fighter cover, would monitor Libyan air attacks on the northern stronghold of Faya Largeau. The Airborne Warning and Control System planes can also be used to control the movements of friendly fighters in air combat.

Habre, who Libya claimed last week had been killed in air raids on Faya Largeau, called for French air support and praised the United States for "responding with firmness to Libyan actions throughout the world."

But, he said at a press conference in the capital, Ndjamena, "We insist that the U.S. government step up its aid" as western support to Chad "is insignificant compared with the scope of Libyan aggression." Officials in Washington said Habre conveyed the same message Friday to U.S. Ambassador Peter Moffat.

"Libya intends to totally destroy Faya Largeau," Habre said. "What is happening there looks like something out of a film--it's a veritable act of genocide. Direct French air intervention is needed to counter the Libyan aggression."

Libya, meanwhile, threatened to turn the Gulf of Sidra, claimed by Col. Muammar Qaddafi's government, into a "sea of blood" to keep out nearby U.S. warships and described an American exercise in the Middle East as "an occupation of Arab land."

Jana, the country's news agency, saying that U.S. ships operating in the central Mediterranean were a threat to Libya's control of the Gulf of Sidra, declared: "The Libyan people will not give up . . . and is prepared to turn it into a sea of blood or die."

In Paris, Defense Minister Charles Hernu and senior aides were reported to be meeting to review the situation in Chad. A government source was quoted by news services as saying that France "cannot remain indifferent to the aggravation of the military situation in Chad."

"The French," said a senior U.S. official in Washington, "are looking very closely at how they should respond. We feel they are very close to deciding. They recognize the extent of the Libyan aggression."

The United States has been urging France for the past week to take a more active role in bolstering Habre against the rebels, but the Socialist government of President Francois Mitterrand is reluctant to commit itself to direct military intervention.

France has announced shipment of $45 million worth of war materiel to Chad in recent weeks but said it is not bound by the terms of a 1976 military cooperation agreement to defend the country, which it ruled as a colony until 1960.

Habre said yesterday that the agreement authorized France "to fly to Chad's support in case of external aggression." He opened his news conference by saying, "Gentlemen, I have not been killed, contrary to what the Libyans have been saying." He said the Libyans had not driven his forces out of Faya Largeau but claimed that their aim was to "raze the town."

President Reagan has authorized $25 million in emergency aid for Chad. Thirty Redeye and Stinger antiaircraft missiles, and three U.S. Army advisers to train Chadian troops in their use, arrived there last week.

The State Department said that the AWACS, whose advanced radar equipment allows them to "see" up to 200 miles, had been moved "to where they could be most useful to help in monitoring the situation in Chad."

Spokeswoman Anita Stockman told The Associated Press that the AWACS would be accompanied by several support aircraft, "including some protective fighter aircraft and tankers." She said the planes were sent from the United States and bases overseas and would not be diverted from U.S.-Egyptian maneuvers now under way in the region. The Pentagon announced last week that two AWACS planes had been sent to Egypt.

The United States, officials said, will replace equipment lost by Habre's forces in recent fighting against the insurgents led by former president Goukouni Oueddei. Trucks are an urgent priority, they said.

The State Department, reporting on the military situation in Chad, said that Libyan and Libyan-supported insurgents were in the "close vicinity" of Faya Largeau.

"While there don't appear to have been any ground actions there in the past few hours, we consider that Faya remains threatened," a U.S. official said. "We also understand that rebel forces have attacked towns in the east."