Lebanese officials appealed urgently today to the United States and the other countries in the multinational peace-keeping force to send more troops to deploy in the mountains overlooking Beirut as fears mounted that Syrian-backed Druze forces and their allies would attempt to push into the beleaguered capital.

The officials warned in a background briefing that Syria is taking advantage of the chaos and violence steadily engulfing the Beirut area to help forces of the Palestine Liberation Organization infiltrate into Beirut. They backed up their claims with aerial photographs and what they described as transcripts of interceptions of radio transmissions.

The unusual public appeal for more assistance reflected fears here that rather than sending in more troops the United States, Italy, France and Britain might withdraw their soldiers as Lebanese strife begins once again to resemble a civil war.

Diplomatic sources in Washington and Paris indicated yesterday that there are no urgent consultations under way on expanding the force and that there has been no formal request from the Lebanese government for an expansion. French Prime Minister Pierre Mauroy pointedly has noted, however, that the French troops were sent to Lebanon to interpose themselves between the Israelis and the Syrians and that the Israeli withdrawal has created a new situation that threatens to involve the multinational force in a full-scale civil war.

Speaking in a television interview Tuesday, Mauroy stopped short of saying that France was reconsidering the role of its troops in Lebanon.

In Washington, congressional sources indicated that legislation authorizing U.S. marines to remain in Lebanon probably will be introduced shortly after Congress returns from its summer recess next Monday, Washington Post staff writer Helen Dewar reported.

While the White House has been reluctant to seek such authorization on its own, sources said it is anxious to avoid a confrontation with Congress on the troops issue and would not necessarily resist a congressional initiative to authorize the continued deployment.

Congressional leaders agreed last Sunday in a meeting with President Reagan to delay any decision until further consultations next week, according to an aide to the leadership.

Meanwhile, Rep. Clarence D. Long (D-Md.), chairman of the House Appropriations subcommittee on foreign operations, scheduled a press conferenece to announce he will try to cut off funding for the marines in Lebanon until Reagan seeks congressional authorization for them to remain. Long plans to introduce a funding cut-off amendment in connection with an urgent omnibus spending bill that must be approved by Oct. 1.

The Lebanese officials said that more than 1,000 Palestinians and leftists were aiding the Moslem Druze in their sectarian battles with Christian Phalangists in the mountains.

Followers of Druze leader Walid Jumblatt in Beirut and in the Syrian capital, Damascus, categorically deny that the PLO or any other non-Druze have assisted in the Druze drive against Christian Phalangist forces in the mountains.

But officials at the presidential palace presented detailed evidence to western journalists today.

They displayed aerial photographs of tanks they said Palestinians had driven into territory vacated by Israel and read messages of what they described as intercepted radio transmissions between two PLO factions, the Democratic Front for the Liberation of Palestine and the Popular Front for the Liberation of Palestine, with their headquarters.

Both groups are closely aligned with Syria and have been opposed to Yasser Arafat's faction in the PLO's internecine fighting.

The messages spoke of their role in fighting with the Druze and of attempts to push to the outskirts of Beirut.

This week's battles, the latest of many in Lebanon's troubled history, center on the Moslem Druze, a mountain sect led by the 36-year-old Jumblatt.

Although much smaller than many of Lebanon's disparate minorities, the Druze are demanding more influence, citing their deep roots in Lebanon's history.

Historically, they have relied on outside powers to come in and help them settle their problems and Jumblatt appears to have cleverly played both the Israelis and Syrians to gain advantage over the dominant Christians.

The Israelis, according to numerous accounts, left the way open for the Druze to take control of the most important strategic positions in the mountains when they abruptly withdrew on Sunday. Syria has been providing Jumblatt with artillery support from positions in Lebanon.

But the question here now is whether he will be able to extricate himself from his alliances to to take advantage of his gains.

"I'm afraid it comes down to brutal, simple terms," said one Western diplomat. "If Jumblatt doesn't do what the Syrians want him to do, well, the Syrians will kill him."

Lebanese who know Jumblatt well worry about his uncompromising zeal in the battle with Christians.

They also worry about help from the PLO in the battles of the past several days, and whether that will bring the Israelis into renewed bombing of Lebanon.

Longtime observers of Lebanese affairs say it is these fears, along with reports of polls from the United States showing growing distaste among the electorate for the Marine role in Lebanon, that appear to be motivating the public appeals by Lebanese officials for more assistance, perhaps in the hope that they will at least be able to keep what they have rather than be left alone.