The Israeli Army has intervened on behalf of Christian Lebanese Forces and the Lebanese Army here to prevent the Druze militia from taking control of the coastal highway leading to the southern suburbs of Beirut and apparently also to assure a Christian-dominated "buffer zone" north of the Awwali River.

An Israeli patrol of eight armored personnel carriers and two Centurion tanks flying big Israeli flags today went about eight miles north of the Israeli Army's Awwali River line to this town on the coastal highway in an operation aimed at "showing presence," according to its commanding officer.

Two American reporters watched as the officer and three aides consulted at length beneath a tree just off the highway with two Christian Phalangist militiamen and three Lebanese Army soldiers about the situation. Afterward, the patrol wound its way several miles inland to an old Israeli Army position to observe the fighting.

The Israeli officer would say nothing further about his mission. But a Druze spokesman in Beirut said later that on Monday the Israelis prevented their militia from reaching the highway when it was within 400 yards of it.

He also charged that the Israeli Army had assisted the Phalangist militia by transporting some of its men to a hill overlooking the contested village of Ain Haour, forcing the Druze to withdraw from there. The village is a few miles inland from here and is now reportedly held jointly by the Lebanese Army and the Christian militia.

The Israelis "stopped us and the next morning they drove in some Lebanese Forces the Christian militia and put them on one of the hills above Ain Haour," the spokesman said.

"It seems they want to be sure no Palestinians pass below Jiye," he said. Jiye, the next coastal town to the south, is two miles from here. "We are assuring them that there are no Palestinians with us," he added without saying how this was being done.

In Jerusalem, Israeli military sources told Washington Post correspondent Edward Walsh that it was "in everyone's interest" to see that Palestinian guerrillas did not gain control of the coastal highway. They said this was one of the main reasons for what they described as "routine patrols" by the Israeli Army north of the Awwali, the line to which it withdrew 10 days ago in its pullback from the Beirut suburbs and the Chouf mountains.

The sources said the patrols would continue "as long as the situation is fluid and there is a possibility of infiltration below Deir Qamar," the Druze-encircled Christian village 10 miles inland from here.

"These are not patrols designed to confront anyone as a fighting force, although they will fight if necessary," the Israeli sources said. "Their purpose is to observe and see there is no change in the situation."

"They also serve as a deterrent to Palestinians coming down the highway," he added.

The area where the Israelis are apparently attempting to establish a buffer zone is known as the Iqlim Kharroub, which has a mixed population of Druze, Sunni Moslems and Maronites.

Travelers from the area say that the Israelis have also helped the Christian militia establish and reinforce itself in Debiyyah, which was earlier under Druze attack.

The Lebanese government and Western diplomatic sources say they are convinced that leftist Palestinian groups are among a number of Syrian-backed militias aiding the Druze in their struggle to assure their control of the mountainous Chouf region overlooking Beirut on the southeast.

They say these groups are involved in the current Druze siege of the mountain town of Suq al Gharb, where the Lebanese Army has been fighting off repeated ground assaults and heavy artillery shelling since Saturday.

While reporters have seen Palestinian guerrillas and leftist Lebanese elements together with the Druze in the area of Alayh and Bhamdun--two towns on the Beirut-to-Damascus highway--their exact role in the actual fighting remains unclear beyond acknowledged artillery support.

The Israeli military sources said there was no official policy of trying to establish a "buffer zone" north of the Awwali but added that "it is in everyone's interest to keep control of the coastal highway."

Nonetheless, what the sources said and the Israeli troops were doing appeared to be aimed at assuring that the Lebanese Army and Christian militia together maintain control of the highway and the immediate heights overlooking it.

Deir Qamar, on the other hand, is well inland, indicating that the Israeli objective is not limited to the highway and the adjoining heights.

That the three are working together to maintain Army and Christian militia control of the area east and south of here seemed evident from the half-hour meeting of their officers, in which they pored over a map. After the patrol's trip inland, they again met in the same spot for 20 minutes.

The Israeli patrol was escorted by a Christian militia jeep and several militiamen served as traffic policemen as it passed through Saadiyat.

The Israeli patrol today saw the Druze shelling of the Christian Phalangist barracks in Michref just east of the coastal town of Damur in the foothills of the Chouf. It appeared to have been hit several times and flames and a huge column of smoke could be seen rising from the area.

The Lebanese Army and Christian militia now seem to be cooperating closely in this area to prevent the Druze from reaching the coastal highway. Both have forces in and around Ain Haour, which leads to the highway, and several other nearby towns. They are also sharing positions in Damur.

In addition, the Lebanese Army is allowing the Christian militia to maintain a checkpoint on the coastal highway outside Damur to check identity papers of everyone traveling into the Beirut area--apparently an attempt to prevent any Druze or other armed elements from entering the capital.

Druze leader Walid Jumblatt has complained that the Lebanese Army has been working hand-in-hand with the Christian militia against the Druze and he has demanded that both leave the Chouf area.

The Lebanese and Israeli governments fear that leftist Lebanese and Palestinian groups will infiltrate Beirut and make an alliance with the Shiite Amal militia against the central government of President Amin Gemayel.