A fragile cease-fire took hold here today in the Chouf mountains overlooking Beirut after the Israeli Army intervened to halt four days of clashes between Moslem Druze and Christian Phalangist militiamen.

Meanwhile, in Bhamdoun, a few miles north of here in Israeli-occupied territory near Syrian lines, an Israeli soldier and a Lebanese civilian reportedly were killed when a bomb exploded in a car. The towns near Syrian lines have been the scene of several attacks in recent weeks, and the Israelis have said that they hold Syria responsible for allowing guerrillas to infiltrate into the area.

It was the first death of an Israeli soldier since Oct. 3, when gunmen ambushed a bus carrying Israeli troops, killing six soldiers and wounding 22. The next day, Israeli warplanes destroyed a Syrian antiaircraft missile launcher in Lebanon.

The Israelis posted tanks and armored vehicles in several villages to end the first serious outbreak of sectarian fighting since the multinational peace-keeping force arrived in Lebanon late last month. The Israelis also set up a meeting between Druze and Phalangist leaders, who agreed on mutual concessions in hope of preventing further clashes, an Israeli military source said.

A senior Lebanese government official told reporters that he thought it was "quite likely" Israel had provoked the fighting.

The official, who requested anonymity, said in a briefing in a Beirut suburb that the Israelis and other foreign forces should leave Lebanon, but he did not spell out why or how the Israelis may have encouraged the clashes.

Reports in the Beirut press have suggested that the Israelis were allowing arms and ammunition to flow into the Chouf area to encourage fighting and thus justify the need for continued Israeli occupation.

The Chouf fighting seemed to demonstrate that Lebanon's central government is not yet capable of ensuring order 15 miles southeast of the capital. The government reportedly considered dispatching the Lebanese Army to the area to restore calm, but the Army has its hands full seeking to establish its authority over Beirut.

The clashes also indicated that President Amin Gemayel cannot restrain the militias of his Christian Phalangist party. The fighting was sparked primarily because of a push by the militias to expand their authority in the Chouf.

In Beirut, the regular Army has not yet begun to search for arms and suspected criminals in East Beirut -- where the Phalangists are strong -- as it did in predominantly Moslem West Beirut.

The Army reinforced positions on the outskirts of East Beirut today and yesterday, and the Lebanese justice minister has said that the searches will begin within two weeks. Phalangist officials say that their militiamen voluntarily will stop wearing uniforms and carrying weapons in East Beirut once the Army moves in.

No gunfire could be heard in this Druze village early this afternoon, and residents said the fighting had stopped at about midday after two Israeli tanks and an armored personnel carrier rolled through. Shops were closed, however, and residents said many persons were in shelters because they feared new fighting.

Tanks, armored vehicles and soldiers were posted in Kfar Matta and Bawharta -- villages where the clashes reportedly were heaviest -- and in two other villages, according to the Israeli military source. The Israelis had sent patrols through the towns during the four days of clashes, but the source said this time the Israeli forces would stay overnight to prevent fighting.

The Beirut newspaper As Safir said 12 people had been killed and 60 wounded on the third day of fighting, but comprehensive casualty reports were not available.

When asked why the Israelis did not move earlier to halt the fighting, the Israeli military source said, "It was a political and not a military decision." He did not elaborate.

At the Druze-Phalangist meeting in Kfar Matta, the two sides agreed in principle on several points to help stop the clashes, the source said. The Druze agreed to let some Christians move back into houses left vacant since the 1975-1976 civil war, while the Phalangists agreed to halt harassment of Druze at roadblocks. Israeli troops may join Phalangists at roadblocks to ensure that Druze are not mistreated, the source said.

The senior Lebanese official said that it was "too soon" to respond to Israel's decision to seek a written commitment from Lebanon that hostile forces would not be allowed to deploy in a strip of territory along the Israeli border.

He suggested that Lebanon would oppose a treaty with Israel, stressing that it was dealing with U.S. special envoy Philip C. Habib on the issue rather than directly with Israel.

He acknowledged, however, that the government was willing to commit itself in some way to guarantee that Israel would be secure against attacks from Lebanese territory.