Israeli soldiers advanced into positions previously occupied by the Palestine Liberation Organization in a southern neighborhood of West Beirut today, setting off a mobilization of the city's heavily armed militias that all but shattered a one-day-old government effort to clear armed men from the streets.

Militiamen exchanged fire with an Israeli unit that moved into Beirut's heavily bombed Bir Hasan district. The push triggered sporadic shooting in which a French Army colonel serving with the U.N. peace-keeping force in southern Lebanon was killed and at least three Lebanese were wounded.

Prime Minister Shafiq Wazzan, who yesterday announced a government plan to remove all armed men from the streets of Moslem West Beirut, protested the Israeli advance to U.S. Ambassador Robert Dillon this afternoon. Wazzan called the move a violation of the U.S.-negotiated accord that provided for the Palestinian evacuation of the city and was to have ended Israel's summer-long siege of West Beirut.

Lebanese national television reported tonight that Wazzan had been promised that Israel would pull out of Bir Hasan by Saturday morning after U.S. and Israeli officials discussed the matter.

An Israeli military spokesman in East Beirut said the soldiers had moved forward about 500 yards into the neighborhood where the United Nations headquarters are located only to protect mine-clearing operations along what had been the PLO's southern perimeter of West Beirut.

The spokesman said these operations were being conducted in the same manner as mine-clearing operations carried out around other parts of the Lebanese capital by the Lebanese Army and the multinational force set up to guarantee the normality of Beirut after the now-completed evacuation of PLO forces and their Syrian allies from the city.

The cease-fire agreement negotiated by U.S. special envoy Philip C. Habib, however, had made no provisions for Israel to take part in mine-clearing operations around the city or for Israeli troops to advance from their previously held lines to do so. The agreement's second article spoke of a "cease-fire in place" that would be "scrupulously observed" by all parties.

The multinational force was specifically charged with interposing itself, with the help of the Lebanese Army, between the Israeli forces and the Moslem and leftist militias -- which had been allied with the Palestinian forces -- left in the city.

According to the plan, the multinational force's Italian troops were to have taken up positions south of the city around Beirut International Airport, one mile south of Bir Hasan, after an Israeli pullback. For reasons that have never been explained, these plans were changed and both the French and Italian troops have taken up positions only across the Green Line dividing East and West Beirut while the 800 U.S. Marines have confined themselves to the Beirut port area. The Italian troops never deployed around the southern perimeter of the city, and Israel has refused to pull back from the airport.

That has left a vacuum around Bir Hasan, a neighborhood of Arab embassies and modern apartment buildings that had been held by forces from Yasser Arafat's Fatah organization.

Today, squads of Israeli infantry moved up from their previous positions just south of Bir Hasan to take up new positions on a bomb-cratered boulevard that leads from the coast east to the Kuwait Embassy, almost on the southern edge of the Shatila refugee camp.

As the Israelis cleared the mines in the area, loud, earthshaking explosions sent up huge plumes of black smoke this afternoon.

Moslem leaders and the various militias who suddenly converged on the area to set up defensive positions were afraid that the mine-clearing operations might be a prelude to an Israeli armored thrust into what is now a lightly defended part of the city.

Militiamen deployed with self-propelled rockets, machine guns and mobile antiaircraft guns and exchanged gunfire with the Israeli force that was estimated to number from 50 to 100 men. Scattered gunfire continued into the night.

Earlier in the day a French lieutenant colonel in the United Nations Interim Force in Lebanon (UNIFIL), who had been at the U.N. headquarters building in Bir Hasan inspecting war damage, was fatally shot in the chest by stray bullets. It was unclear who fired the shots.

The state radio reported an unspecified number of people killed and wounded after a car bomb exploded near an Israeli checkpoint in Deir el Kamar, a town in a predominantly Christian area 13 miles southeast of here. Three Israeli soldiers were among the wounded and were flown by helicopter to Israel for treatment, the radio said.

The Israeli move into Bir Hasan appeared to harm government hopes for demilitarizing the streets of West Beirut. On Thursday, national police had deployed into West Beirut to begin policing duties that were to include the arrest of anyone caught carrying a gun in public or displaying weapons in the city streets.

The PLO, in apparent violation of the Habib accord, gave its heavy weapons to the Moslem and leftist militias. The accords had stipulated that the PLO heavy weapons were to be turned over to the Lebanese Army. But West Beirut's Moslems consider the Army a tool of their long-time Christian antagonists.

During the night, rival militias, one Kurdish, the other Shiite, battled with heavy machine guns and rockets in the downtown Kantari district, apparently because of a personal feud between their leaders. The fighting later moved down into the old Jewish quarter of Wadi Abu Jamil, and Beirut state radio reported that three people were killed and three wounded in the fighting.