The Israeli Army withdrew from its last two positions inside West Beirut today and also agreed to a total evacuation of the international airport, clearing the way for the arrival of 1,200 U.S. Marines Wednesday.

U.S. envoy Morris Draper met with President Amin Gemayel during the day to inform him of the complete Israeli pullout. The agreement came after a day of hard bargaining among U.S., Israeli and Lebanese authorities over Israel's insistence that it be allowed to retain a presence at the airport and use it for civilian and military flights.

The Israeli stand had thrown into confusion the question of whether the Marines would go ahead and land, since Washington's position remained that it would not introduce troops into the area until Israeli forces withdrew.

An indication that agreement had been reached came tonight when Lebanese Public Works Minister Elias Herawi announced on state-run television that the airport would reopen to civilian traffic Thursday at 10 a.m. after being closed since the onset of the Israeli invasion of Lebanon June 6.

Lebanese authorities, along with the United States and the other members of the international force, France and Italy, had sought a complete withdrawal of the Israelis as a condition to reopening the airport.

The Marines are the last units of the multinational peace-keeping force to arrive here and will join 1,100 French paratroopers and as many Italian troops in helping the Lebanese Army to assure law and order in West Beirut following the massacre of hundreds of Palestinian refugees in their camps here Sept. 16 through 18.

A Lebanese government commission charged with investigating the massacre held its first meeting, Reuter reported. The chairman, military prosecutor Assad Jermanous, said it had decided to call 20 witnesses to give testimony Wednesday.

The U.S. contingent, initially due to arrive here Sunday, will be primarily responsible for security in and around the airport. Israeli Army spokesmen here said they understood the U.S. Marines would come ashore at the port, the airport and the beaches adjacent to it sometime during the next 48 hours.

Israel's pullout from its last two positions in West Beirut proper -- at the port and the Gallerie Semaan crossing -- came this morning shortly after a meeting between special envoy Draper and Maj. Gen. Amir Drori, head of the Israeli northern command.

An Israeli Army spokesman in East Beirut said at the time that "it was agreed" the Army would continue to use the southern part of one of the airport's two runways at least "for the next few days."

The spokesman said the agreement had been worked out between Israeli and Lebanese officials and insisted there had been no "negotiations" with the Americans over it. He described the Draper-Drori meeting as only "an exchange of information" and denied there was any linkage between the Israeli final withdrawal and the arrival of U.S. Marines.

"Our position on the ground is a matter between the Lebanese and Israeli governments," he said. "It is not a matter of us negotiating with the Americans."

The military command in Tel Aviv said guards shot and wounded eight prisoners while breaking up a riot Tuesday at the Israeli prison detention camp for suspected Palestinian guerrillas, Associated Press reported.

The command also announced that Israeli troops had completed the removal of arms and ammunition from Palestine Liberation Organization strongholds in West Beirut. The materiel included: 520 tons of ammunition, 23 tanks and armored personnel carriers, 200 other vehicles, 80 cannon and mortars, 75 rocket-propelled grenade launchers and 5,000 small arms including rifles, machine guns and pistols, the statement said.

The Israelis have not agreed to pull out of Christian East Beirut until the end of this week.

Edmond Ghosn, the Lebanese airport director, told reporters that the airport was ready for reopening "whenever they give the word."

He said the Middle East Airlines, the Lebanese national carrier, had told him it would land its first plane within 24 hours after the decision to open the airport was announced.

Workmen were busy today finishing repairs on the main terminal building, which appeared in fairly good shape despite days of fighting around it this past summer. The wreckage of one of four destroyed MEA planes was still visible on the tarmac as well as a mobile staircase used to load passengers.

In the distance, Israelis could be seen evacuating their main command post near the point where the airport's two runways cross.

Meanwhile, French and Italian paratroopers and marines continued their deployment in the two Palestinian camps of Sabra and Shatila where the massacres took place.

The French and Italians have been given primary responsibility for security in and around the camps, while the Lebanese Army has now established its presence throughout Moslem West Beirut.

Moslem militamen were not in evidence inthe western sector -- for the first time after eight years of political turmoil here. But Christian militamen can still be seen manning checkpoints and inspecting papers in the eastern sector.

The Palestinian camps were active today, with bulldozers flattening all badly damaged homes at the southern end of Shatila and clearing the land. Refugees hope new homes will be erected, even if they are tents.

Small groups of Palestinian men, women and children watched silently as the wreckers, bulldozers and trucks brought down and carted away the remains of their homes. Some vehicles were hauling water from a broken water pipe sticking out of the ground.

"We want to stay," declared Said Ghalib, a refugee who lost his brother and his four children in the massacre. "But we are waiting for the government to decide."

The government has not even decided yet whether it will allow tents to be put up to house the homeless residents of Shatila on a temporary basis.A plan is being discussed to move all the Palestinian refugees away from the city.

It is still not clear how many Palestinians and Lebanese civilians were killed during the 36-hour rampage by Christian militiamen through the camps.

Ghassan Ibrahim, head of the Lebanese civil defense unit responsible for collecting the bodies, said his group had counted 480 dead.

He said four more bodies had been dug up Monday on the edge of the sports stadium adjacent to Shatila camp. The International Red Cross is no longer involved in the hunt for bodies, but when it stopped a few days ago it had discovered 320 bodies in and around the two camps.

Most of the dead have been buried in a mass grave at the southern entrance to Shatila camp. Two wreaths have been placed on piles of dirt at the site, one from the Palestine Liberation Organization with the words, "Long live our dead."

The other, from the "people of Shatila," is addressed to Israeli Defense Minister Ariel Sharon. It says:

"Sharon. The massacre of Sabra and Shatila will increase our determination to fight for the rights of the people of Sabra and Shatila."