The multinational peacekeeping force now heading for Beirut, including 800 U.S. Marines, is scheduled to be deployed this weekend whether or not Israeli forces have completed their pullout from the Lebanese capital, the State Department said yesterday.

"It is our expectation and hope that the Israelis would be gone by the time the Marines land," State Department spokesman John Hughes said. When pressed as to what might happen if they have not pulled out, as President Reagan has demanded, Hughes said, "Our plans are to go ahead."

The force's French units began arriving off the Beirut port yesterday and U.S. units are to arrive today, but negotiators in Beirut and Washington yesterday still had not resolved exactly where the troops were to be stationed or what they were supposed to do.

The force is to be somewhat larger than originally suggested -- about 3,000 men, U.S. officials said -- and there have been indications that some contingents will be more heavily armed than on their last tour in Beirut, though the U.S. troops put ashore will carry the same light weapons as before, a Pentagon spokesman said yesterday.

Administration sources indicated that the Marines would first move to secure the port area, then move south along the coast to the airport, which would become their logistical base.

The participating French and Italian units, which apparently are to be more heavily armed than the Marines, likely will move inland to areas near the Green Line separating predominantly Moslem West Beirut and predominantly Christian East Beirut.

The French forces are expected to land this morning but will go straight to the French Embassy, it was reported from Beirut. They will then link up with the U.S. and Italian troops when they land.

The French and Italian units are to number 1,100 men each, far larger than the contingents supplied to the first multinational force that landed in Beirut to supervise the withdrawal of Palestine Liberation Forces.

Pentagon spokesman Henry Catto said yesterday that, while the U.S. contingent sent ashore will number 800, the same as in the first force, an additional 1,000 Marines will be on ships offshore.

The Marines will carry personal weapons and machine guns, but heavier weaponry will be kept on the waiting ships where it can be called upon "quickly if necessary," according to an administration source.

The Italians, however, are expected to be equipped with armored personnel carriers, tanks and crew-served weapons, reflecting the different missions the multinational force faces, according to a diplomatic source.

The revival of the multinational force was announced Monday following weekend revelations that Christian forces allied with the Israelis had massacred uncounted numbers of Palestinians in refugee camps.

Reagan stressed then and officials have continued to emphasize that it is the U.S. goal to use the troops as a stabilizing force to allow the Lebanese army and police to take over police functions.

Italian and French officials talk of the same goals, but also are more outspoken about preventing further deaths in the civilian population. "This mission is to avoid the recurrence of what we have seen this weekend, to protect menaced individuals," one diplomat said.

Part of the negotiations apparently involve whether the troops in the force will be stationary, as they generally were during their first mission, or will patrol to provide a more visible presence, according to European diplomatic sources, who hinted that a somewhat more visible role is possible.

Lebanese officials are pressing for the widest possible presence for the force, including having units stationed in the Palestinian camps and throughout West Beirut, Washington Post correspondent David B. Ottaway reported from the Lebanese capital. U.S. officials have rejected proposals to have the Marines enter the camps.

Discussions also were continuing in Beirut on how long the force would stay in Beirut and what its command structure would be, Ottaway reported.

Israeli forces continued their phased withdrawal from West Beirut yesterday, but the Israelis still were said to be pressing for the right to keep small units in the city and to be reserving the right to patrol throughout West Beirut.

Special negotiator Morris Draper and his predecessor, Philip C. Habib, were in Israel yesterday to take up the questions of Israeli withdrawal, State Department officials said.

Late yesterday afternoon, a half-dozen Israeli armored personnel carriers could still be see parked in the port area near where the French forces are expected to land this morning, Ottaway reported.