Palestinian guerrillas unleashed artillery fire on two Norwegian platoons of the U.N. peacekeeping force in southern Lebanon yesterday, and the Norwegians temporarily withdrew from their position, U.N. officials in Beirut reported.

There were no confirmed reports of casualties, and the Norwegians returned several hours later to their position near the strategic Khardali Bridge across the Litani River, U.N. officials said. The river marks the limit of Israeli-occupied Lebanon following last month's invasion.

The firing came from the 12th Century Crusader castle at Beaufort, a Palestinian-controlled position about seven miles southwest of where the Norwegians were encamped.

United Press International quoted U.N. sources in Beirut as saying the Norwegians responded with light and medium machinegun fire and that a duel with the Palestinians continued for three hours. U.N. spokesmen in Jerusalem and New York said, however, that there was no indication that the Palestinian gunfire was returned.

There was no immediate indication from southern Lebanon of what prompted the attack, but diplomats in Beirut suggested the firing may have come from radical Palestine Liberation Organization factions who believe the U.N. force is not ensuring an Israeli withdrawal.

U.N. officials said there has been "great activity and tension" in the area, but the incident was the first direct assault targeted specifically on the peackeeping forces.

Since the first of the U.N. forces arrived in southern Lebanon March 23, a Swedish warrant officer was killed by a land mine last month and French troops were harassed by crossfire Wednesday. The Norwegians are between the Palestinians and right-wing Lebanese Christian militiamen and have come under desultory fire from both sides, but never before under a concentrated artillery barrage.

A U.N. spokesman in Beirut said the Norwegians had no choice but to withdraw. "As you know, our forces are not heavily armed. They are just armed with light weapons for self defense. So if something happens, they cannot cope with it," he said.

Meanwhile, U.N. Secretary-General Kurt Waldheim termed as "inadequate" an Israeli plan for a two-stage withdrawal of its forces in southern Lebanon. In a statement issued in New York, Waldheim said the plan falls short of a Security Council resolution calling for withdrawal of all Israeli forces in Lebanon.

Israel on Thursday informed the United Nations it will begin a partial withdrawal next week along the eastern half of Israel's front in Lebanon. In Beirut, a PLO spokesman brushed aside the Israeli plan, describing it as a "trick."

It also was reported that the PLO had agreed to return the bodies of the Israeli soldiers who were killed Wednesday when they wandered into Palestinian-held territory near the port city of Tyre. The Palestinians said they had five bodies, although the Israeli account of the incident placed the known dead at three, with two soldiers listed as missing.

The United Nations said the Palestinians had agreed to return the bodies through the International Red Cross.*