The Palestinian guerrillas are studying a proposal to allow a token U.N. peacekeeping force to be stationed north of the Litani River, the last sizable area in Lebanon still under commando control, it was learned yesterday.

Palestinian commander Yasser Arafat agreed to consider the proposal, which U.N. Secretary General Kurt Waldheim transmitted on behalf of the Lebanese government during his brief visit to Beirut on Monday.

Even if only a token force - perhaps a few U.N. observers - were allowed in these areas north of the Litani, analysts are convinced they could serve as a precedent for allowing some form of official Lebanese presence to follow.

Both the Lebanese and Israeli governments are known to have asked the United Nations to take full control of these areas - plus the Mediterranean port of Tyre - which remained in Palestinian hands throughout the March invasion of southern Lebanon by Israeli troops.

The Lebanese army collapsed in disarray during the civil war, and the government has not had any authoratative presence since.

The peacekeeping proposal was revealed as tension mounted in Beirut. Two Christiangendarmes were killed under mysterious circumstances inan area dividing eastern, Christian Beirut from its predominantly Moslem half.

Adding to the feeling of unease was rare news conference held by Ibrahim Koleilat, leader of a left wing Moslem militia unit called the Morabitoun, which played a major role in the 1975-1976 civil war.

He denounced the U.N. peacekeeping force as an occupation army> and attacked Libya and other radical Arab states for not aiding the Palestiniants during the Israeli invasion last month. He also criticized Arafat indirectly for being too moderate, and warned the Christians his forces would retaliate if attacked.

A sure sign that Christian militia leaders were concerned by the mood was provided by a visit which militia chieftain Beohir Gemayel paid to the Syrian commander of Arab peace-keeping forces in Ain Rummaneh, scene of the major fighting between their respective forces last week.

Earlier in the day, the Christian militia announced that it was stepping up its patrols within its own areas and taking other measures, which suggested its forces were on alert.

The Beirut tension all but obscured the potentially major significance of the proposal concerning the area north of the Litani. Specifically concerned, according to commando sources, were the Crusader castle of Beaufort, a nearby crossroads and the once-prosperous, but now damaged and largely deserted, town of Nabatiyeh.