Both Syria and Israel recently have accused the other of planning an offensive in the Bekaa, where a tense truce generally has prevailed since the summer apart from individual guerrilla raids and Israeli air attacks on Syrian surface-to-air missile batteries.

An Israeli military spokesman based in Baabda, a suburb of Beirut, said the missiles were fired from the Syrian side of the border. Israel repeatedly has attacked Syrian antiaircraft missiles in eastern Lebanon but so far has not struck across the border.

The incident appeared likely to slow efforts by U.S. envoy Morris Draper to arrange a withdrawal of Israeli, Syrian and Palestinian forces from the country. The Lebanese government, in a concession to the Israelis, agreed to assign a civilian to a team of military officers who will carry out direct talks with the Israelis on the pullout.

Syria made no immediate statement, but Damascus radio reported without comment an Israeli announcement of the incident, Reuter reported.

Meanwhile, new clashes flared between Moslem Druze and Christian Phalangist militias in the Israeli-occupied mountains southeast of the capital. Israeli military sources said that the fighting had slackened after several Israeli armored vehicles moved into one village to enforce a cease-fire.

Lebanese Prime Minister Shafiq Wazzan said Draper had informed him that Israel had accepted Lebanon's proposal to carry out future talks on the withdrawal through an existing military liaison committee expanded to include at least one civilian legal adviser and U.S. representatives. The Lebanese Cabinet agreed tonight to endorse the plan, arranged by Draper in his shuttle between Beirut and Jerusalem, authoritative government sources said.

Israel has pressed for the highest possible representation on the committee as a step toward normal diplomatic relations. The Lebanese delegation still will be chaired by a military officer and may be limited to a single civilian as legal counsel at first, the government sources said.

The panel will consider arrangements for the first phase of the withdrawal of Israeli forces, currently on the southern and eastern outskirts of the capital. Later it will discuss Israel's desire for guarantees that southern Lebanon will not be used for attacks against Israel, the sources said.

The fighting in the mountainous Alayh district overlooking the capital threatened to disrupt a truce established by the Israelis on Oct. 15 after four days of fighting that claimed at least five lives. It erupted a day after gunmen of the Druze militia ambushed and killed a Lebanese Army soldier and wounded three others.

The soldier killed yesterday was the first Lebanese Army casualty in the area since the Army replaced Israeli troops as peace-keepers in two villages. The Army's movement into the area was seen as a test of its capabilities following years of ineffectiveness.