President Francois Mitterrand indicated today that France is prepared to join an expanded international peace-keeping force if the Lebanese government requests such a unit as part of an effort to get Israel to withdraw.

Mitterrand, speaking in an interview immediately after he had met with Saudi Arabian Prince Saud Faisal here, declined to discuss specifically reports that a new peace-keeping unit modeled after the multinational force in the Sinai is being discussed as a possible replacement for the United Nations force that Israeli troops quickly overran in launching their invasion Sunday.

"I don't know what force will be created. In any case, we will participate in any international project," Mitterrand said. "We have not received any specific proposal. But France will participate in any international presence desired by the Lebanese government and approved by the United Nations."

France, which played a key role in the decision by European countries to join the Sinai force organized by the United Nations under the Camp David accords, has supplied 1,300 of the 7,000 troops in the current U.N. force stationed in southern Lebanon.

Palestine Liberation Organization leader Yasser Arafat this week assailed those troops, known as the U.N. Interim Force in Lebanon (UNIFIL). He accused them of facilitating the Israeli invasion and of "collaborating with the Israeli troops." But Secretary General Javier Perez de Cuellar asserted that the UNIFIL forces had faithfully remained in their positions and had attempted to block the Israel advance until "their safety was seriously imperiled."

Israel repeatedly has charged that the U.N. forces were ineffective in keeping the peace in the frontier region and had not stopped Palestinian terrorist movements.

Diplomatic sources reported here that France already has begun studying the possibility of increasing its troops in the U.N. force in any case.

Mitterrand, who was the first French president in history to visit Israel this March and who shifted his country's once strong opposition to Israel to a far more sympathetic attitude, repeated his condemnations of the Israeli invasion in even sharper terms.

"Israel can't think that it can solve all its problems by military means," Mitterrand declared in calling for an Israeli withdrawal from Lebanon.

Prince Saud, Saudi Arabia's foreign minister, is believed to have stressed in meetings in Bonn with President Reagan and British Prime Minister Margaret Thatcher, as well as in his talks here, that the Israeli invasion of Lebanon and the continuing Iranian rout of the Iraqi Army could cause a broader explosion in the Middle East that would draw the United States and the Soviet Union into direct conflict