The two U.S. airborne warning and control system (AWACS) aircraft sent to Sudan to monitor Libyan bombing of neighboring Chad will not be used unless France deploys planes in the central African country, Reagan administration officials said yesterday.

The AWACS planes and eight F15 fighter escorts were still on the ground in Khartoum yesterday as a third airlift of U.S. military equipment began arriving in Ndjamena, Chad's capital, to replenish supplies in the six-week-old battle with Libyan-backed insurgents.

A Pentagon spokesman, Brig. Gen. W.C. Cousland, said that some American soldiers--fewer than six--had gone to Ndjamena to unload and assemble the new equipment.

Diplomatic sources yesterday disclosed that the Senegalese capital of Dakar is being used as a staging post for the U.S. airlift.

The White House, meanwhile, announced that the United States had agreed to provide air transport to Chad for 800 Zairean troops. Zaire's President Mobutu Sese Seko, who visited Washington last week, previously sent 1,800 men to Chad.

U.S. officials welcomed France's decision to send about 180 advisers to Chad, but said the question of the Libyan bombing raids would remain the key factor in deciding further U.S. and French responses to the crisis.

"It would appear to be another step in the evolution of the idea" that the French "must take the lead," one official said.

Concern yesterday focused around the northern Chadian oasis of Faya Largeau, where Libyan and rebel forces were "poised for an offensive," State Department spokesman John Hughes said.

Hughes could not confirm reports of additional Libyan air raids on Faya Largeau since Friday.

The White House, meanwhile, underlined U.S. concern about the situation by strongly attacking Libyan leader Muammar Qaddafi for his support of the armed rebellion against the Chadian government of President Hissene Habre.

"Libya would like to overturn that government and substitute its surrogate . . . ," said presidential spokesman Larry Speakes. "Were this to happen--if Qaddafi were able to set up an established government simply by using his overwhelming military might to do so--this would have consequences beyond the borders of Chad."

Speakes described the situation at Faya Largeau as "serious and threatening."

The crisis in Chad is expected to figure prominently in talks here this week with President Abdou Diouf of Senegal. Diouf, described by senior administration officials as "the most credible of the younger-generation leaders of Francophone Africa," arrived in Washington yesterday and is to meet with President Reagan this morning.

The diplomatic sources also said that Senegal, a former French colony, has been active in persuading a reluctant socialist government in Paris "to play its proper role" in helping defend Chad.

Although the United States has publicly praised French support for Chad, officials have privately expressed irritation that Paris has refrained thus far from providing air cover to protect Chadian forces from the Libyan bombing.

The AWACS planes, which were deployed in part to convince Paris of the seriousness of U.S. intentions, will not be used unless the French send warplanes, U.S. officials said. "The AWACS can only do half their job if there are no attack aircraft," said one Pentagon source.

Officials said the latest airlift to Chad includes vehicles, clothing, field equipment, repair materials and spare parts. There also was an unspecified quantity of 106-mm recoilless anti-tank rifles and ammunition.

Reagan, who Speakes said is directing U.S. policy regarding Chad, has authorized $25 million in emergency aid for that country from a special fund controlled by the Foreign Assistance Act.

He told Congress Monday in a letter that it was not possible to predict how long the AWACS, F15s and other support aircraft would remain in the region, but that the planes and the 550 personnel with them would remain for "only a limited period to meet the urgent requirements posed by the present situation."