Senegal President Abdou Diouf yesterday called on the United States and France to increase their assistance to Chad "rapidly" amid reports of a successful attack by Libyan-backed rebels on a key government stronghold in the north of the central African country.

U.S. officials, commenting that the situation was still fluid, would not say whether there was a commitment to further aid but indicated that two airborne warning and control system (AWACS) planes may soon be used inside the airspace of neighboring Sudan to monitor Libyan moves in Chad.

"I'm sure we won't just leave them on the ground in Khartoum," one official said. Administration sources had indicated earlier that the AWACS planes would not be used without the deployment of French warplanes to deter Libyan air attacks.

Diouf, who met with President Reagan for two hours at the White House, later told editors and reporters at The Washington Post that "We must stop the Chadian adventure. Otherwise we shall see it being repeated in other countries."

The Senegalese president praised France and the United States for aiding the government of Chad's President Hissene Habre, but said that "very much more must be done as rapidly as possible. Habre must call on his friends to help repel the aggression. The problem is caused by the actions of external forces."

Diouf said at the White House that he and Reagan had agreed "to pursue and intensify our consul- tation in order to find the most effective solutions in the interests of peace and international security."

Neither leader made direct reference to Chad in statements after their talks, but a senior State Department official said later that they had discussed "the challenge that Qaddafi of Libya poses in Africa, including Chad."

The United States has already authorized $25 million in emergen- cy military aid to the war-torn country.

The Senegalese leader, who is widely respected by administration officials, began his first round of talks here against a background of increasing U.S. concern and some confusion about the situation in Chad.

The State Department and the Pentagon were unable to confirm reports of the fall of the oasis town of Faya Largeau to Libyan forces and the Chadian rebels they have been backing in a six-week offensive against the Habre government.

"If it were true, it certainly would not be good news, but it doesn't mean the battle for Chad is over," said State Department spokesman John Hughes. "We continue to be deeply concerned about the Libyan aggression and the blatant military intervention."

Another official, one of several apparently considering the consequences of the loss of the town, said, "Faya Largeau is very important, but it's not the only town in Chad."

Speaking before Diouf's arrival, this official said that Senegal "would like to see Qaddafi stopped. He is regarded unambiguously as a threat. They would not like Mr. Qaddafi to own Chad, nor would anyone else in the neighborhood."

Reagan administration sources said that one difficulty in assessing the situation on the ground was that there were conflicting reports from different American intelligence and diplomatic sources monitoring the crisis.

Diouf, whose visit here has been overshadowed by the crisis in Chad, stressed in his visit to The Washington Post the importance of the recognition by the Organization of African Unity of Habre as the legitimate ruler of the country.

Senegal, which severed diplomatic relations with Libya in 1980, fears that a dangerous precedent will be set if Qaddafi succeeds in Chad, Diouf said.

He warned against a possible partition of the country, saying, "If you choose the easy way out there will be no territorial integrity for any African states."