French warplanes fired on artillery batteries in the mountains east of Beirut today after French troops in the multinational peace-keeping force were shelled and four soldiers were injured.

The attack--the first combat use of air power by the multinational force--came after several stern warnings to Syria and the Druze militia fighting the Lebanese Army that France would no longer tolerate the shelling of its troops here, and after a minor diplomatic tiff between Paris and Washington over which country would defend the 2,000-man French contingent against further attacks.

A statement issued in Paris said French Defense Minister Charles Hernu had ordered French commanders here "to make use of our right to legitimate self-defense and to reply against the batteries which have targeted French interests in Beirut."

Earlier, the French had gone to some lengths to disassociate themselves from the U.S. decision to use naval guns to silence Syrian and Druze batteries firing on U.S. Marine positions and in support of the Lebanese Army fighting to hold the strategic mountain town of Suq al Gharb.

The French also had objected vehemently when President Reagan offered to put American offshore firepower at the disposal of the entire multinational force, saying France could protect its own troops and wanted to remain neutral in the internal Lebanese conflict.

Now, however, the French seem to have accepted the need for firing on Syrian and Druze artillery batteries in the mountains even if this indirectly aligns France with the U.S. policy of providing more open support for the Lebanese Army.

Few details were available here tonight about the French retaliatory action. But various western diplomatic sources said four Super Etendard fighters from the aircraft carrier Foch were involved in the operation, with two attacking batteries in Syrian-controlled territory while the other two provided protective cover.

One report said the French warplanes attacked batteries around Duhur ash Shuwayr in the High Metn area. If true, this would mean they very likely hit Syrian batteries, as the Syrian Army has a strong presence there.

Other reports said they attacked 130-mm artillery batteries even farther east around the mountain known as Dahr al Baydar, north of the Beirut-to-Damascus highway, and Ayn Darah, a few miles to the south, both deep inside Syrian-held territory.

Earlier, Syria warned that it would strike back at the U.S. Sixth Fleet if its positions were attacked by American air or naval fire but said nothing about its attitude toward possible French retaliation.

Meanwhile, rumors of an imminent cease-fire again swept the capital because of the intensive diplomatic activity in Damascus today. U.S. special envoy Robert C. McFarlane met with Syrian Foreign Minister Abdel Halim Khaddam and Druze leader Walid Jumblatt. And here in Beirut Richard Fairbanks, an aide to McFarlane, held talks with President Amin Gemayel.

The Phalangist militia radio tonight also reported that Lebanese Foreign Minister Elie Salem was leaving Friday for Washington with a special message for Secretary of State George P. Shultz, but there was no confirmation of this report.

In addition, Saudi mediator Prince Bandar Sultan was due back in Damascus tonight to receive Syria's answer to Saudi-proposed terms for a cease-fire and a national dialogue to reconcile feuding Lebanese leaders.

But there was still no indication early this evening that the Syrians and Lebanese had overcome their remaining differences, particularly about who should represent the Lebanese government at the negotiating table.

Syria has objected to the presence of Prime Minister Shafiq Wazzan and the speaker of parliament, Kamal Assad, while President Gemayel has insisted on his right to decide who will represent the government. At issue is Syria's attempt to regain its former leverage over the Lebanese government and the latter's effort to establish its independence.

Gemayel was reported to have proposed that delegations rather than individuals make up the reconciliation committee and that each delegation head determine who would accompany him. It was not known whether Syria had rejected this approach, which would still allow Gemayel to bring Wazzan and Assad to the negotiating table.

Also apparently still to be settled are the specific powers of U.N. observers and 500 French and Italian officers who might be sent into the fighting area to oversee the cease-fire. One key issue is understood to be whether they would only observe and report violations to a mixed Army-militia committee or would be empowered to enforce the cease-fire with military means if necessary.

Today's shelling of the capital area also affected the Italian contingent of the multinational force, with nine artillery and rocket shells falling inside the compound of 450 Italian paratroopers in the Hazmieh district of east Beirut. Two of the shells scored direct hits on ammunition-laden trucks, setting off a gigantic explosion but not causing any casualties.

The Italians, who have just flown their own warplanes to the British base at Akrotiri on Cyprus, did not respond with gunfire although they have a destroyer and frigate standing off the coast.

Italian spokesman Capt. Corrado Cantatore said, "We don't believe they were trying to hit us." But reporters who visited the scene of the explosion, involving altogether 10 trucks loaded with ammunition, saw no Lebanese Army or Christian Phalangist militia targets in the immediate vicinity.

Indications were that the Italian government still has not made up its mind whether to respond in the same manner as the United States, and now France, to the continuing attacks on its troops' positions.

In other fighting Thursday, two French soldiers were wounded by a grenade attack in Beirut, The Associated Press reported.

Meanwhile, 600 to 800 Druze civilians paraded through the streets of downtown Beirut today and demonstrated near the U.S. Embassy to protest the escalating American involvement in the war on the side of the central Lebanese government and its army.

The demonstration, believed to be the first by Lebanese Druze in recent times, took place as Druze and Syrian batteries were shelling east and west Beirut from the mountains.

The Druze men, women and children marched in an extremely tense atmosphere with hundreds of heavily armed soldiers, some standing on rooftops, closely guarding the route against possible sniper fire or bomb attack.

The demonstrators, many of them American-educated or with relatives in the United States, carried signs such as "Lebanon . . . Another Vietnam" and "Wage Peace, Not War."

A line of soldiers blocked the street in front of the British Embassy, temporarily housing part of the U.S. mission, and halted the marchers there.

To the apparent relief of both demonstrators and the authorities, no incident occurred and the Druze dispersed quietly after delivering a protest letter to Robert Pugh, the U.S. chief of mission, at an annex building next to the British Embassy.

The thrust of the message was that the United States was taking sides in an internal Lebanese conflict and becoming increasingly involved in a war being waged against the Druze people by a Christian-dominated government and army.

"We would like the government of the United States to help in every way possible to arrive at a cease-fire except gunboat diplomacy," said Farouk Abi Khauzam, an American-educated professor and former Cornell University lecturer who led the delegation into the U.S. mission.

Khauzam said he had conveyed the Druze fear that the escalating American involvement in the war would only provoke more outside intervention and "make the crisis even more complicated."

Another distraught American-educated Druze protester, Khaled Ahmed Tahi, said that the United States was "destroying hundreds of years of goodwill in Lebanon" through its present policy here. "I never thought America would bomb us. Never. Never," he said.

Just as the marchers reached the temporary U.S. mission, eight or nine marines from the USS Tarawa strolled by the seaside walkway in front of the building. No one seemed to recognize them despite their shaved heads and bare chests and they passed by undisturbed.