Intensive negotiations continued today toward a cease-fire in the mountain fighting between Christian and Druze militias as reports of yet another massacre reached the capital and concern mounted for the fate of tens of thousands of Christians trapped in a Druze-encircled village.

Official sources said early today that the Lebanese government was waiting to hear whether a modified "peace plan" it had proposed and that special Saudi envoy Prince Bandar had taken to Damascus last night was acceptable to Syria and to its ally, Druze leader Walid Jumblatt.

The revised plan, first worked out in Paris a week before the Israeli pullback Sept. 4 but never implemented, calls for an immediate cease-fire policed by U.N. observers, the entry of the Lebanese Army into the contested Chouf mountains southeast of the capital and a meeting of this country's main political leaders to discuss a solution to its eight-year-old political impasse.

The sources said Lebanon had rejected "radical" Syrian demands for what were believed to be the evacuation of the Lebanese Army from the Chouf and a new Lebanese government under a Syrian-selected prime minister.

Only "slight changes" were proposed in the original Paris plan, they said, to include among other things "all axes and points of friction" throughout the country in the cease-fire and guarantees for civilians to return to their homes and for relief operations to be carried out freely.

The sources admitted it was "quite likely" Syria and Jumblatt would not accept the new Lebanese-proposed version of the peace plan.

Reports from Damascus, where Bandar met today with Syrian Foreign Minister Abdel Halim Khaddam and Jumblatt, said the Saudi envoy was already on his way back to Beirut with "new conditions" posed by the Druze leader for a cease-fire.

Details of these conditions were not immediately available but a Lebanese political leader who spoke by telephone to Jumblatt late last night said he was still demanding that the Lebanese Army withdraw from the few positions it now holds in the contested mountain area overlooking the capital.

At a press conference, Shiite Moslem leader Nabih Berri said Jumblatt had told him he was "ready for reconciliation" but continued to have one condition: "He asks the Lebanese Army to withdraw from the Chouf but not forever."

The Beirut daily An Nahar also reported today that Syria was asking for a new government headed by Syrian-backed Sunni leader Rashid Karami, a former prime minster and part of the opposition National Salvation Front to which Jumblatt also belongs.

Since neither condition is likely to be accepted by President Amin Gemayel, a Christian, it did not appear that the four-point peace plan would be accepted in its present form or a cease-fire would take effect.

But the Lebanese reply to Jumblatt's "new conditions" was to be delivered to Damascus tonight by a Lebanese businessman, Rafiq Hariri, who has also become involved in the diplomacy to end the fighting.

Special U.S. envoy Robert C. McFarlane has also been shuttling between Beirut and Damascus trying to help arrange a cease-fire and a political compromise.

There was a relative lull in the mountain fighting today and only brief shelling of the multinational peace-keeping force stationed here. Both French and American troops of the 5,400-man force have been under fire repeatedly during the past week and two U.S. marines were killed Tuesday in shelling.

Two American F14 fighters from the aircraft carrier Eisenhower again flew over the capital and mountains in the afternoon on what were believed to be reconnaissance flights but were officially described as "tactical missions."

The main concern of the Lebanese government and Christian Phalanagist militia today was the fate of 25,000 to 40,000 Christian refugees in the village of Deir Qamar who have been cut off from food and water supplies for a week now.

An attempt by the International Red Cross to take a convoy of relief supplies yesterday was blocked when Druze militamen refused to allow it to enter the village, which is surrounded by the Druze.

Official sources said the government has asked the multinational force if it could help the refugees, adding that "we are rapidly approaching a tragedy there" and "we have very little time left."

Authorities fear that the Druze militiamen will storm the isolated village and massacre the refugees, who have fled from earlier fighting in other villages to the north.

The Druze and Christian communities have a 300-year history of periodic massacres against one another and memories of this bloody past have conditioned each side to expect the worst of the other.

There have already been reports of six massacres, half committed by Druze and half by Christians, the latest of which was said to have occurred today in Bire, six miles northeast of Deir Qamar. No outsiders have witnessed any of the alleged atrocities, making it impossible to determine what really happened.

The official Beirut radio said 50 persons were killed in Bire. The Phalangist radio put the known total at 64, including 14 who reportedly died while hiding in a church, and it said the toll might top 100.

But the Druze Progressive Socialist Party tonight denied the report and said "the few killed" were Christian militamen "who were dominating the village and terrorizing the population." It called on the International Red Cross to verify this as well as Christian allegations that the Druze were holding some residents hostage.

The Druze, who regard the Chouf as their exclusive homeland, have been making steady progress this past week toward driving the Christian militia from the area.

One of the key Druze conditions for a cease-fire is that the Phalangist militia leave the Chouf entirely. It is unclear whether they will eventually agree to allow the regular Lebanese Army to move into even these evacuated Phalangist positions as part of a political compromise. They have been shelling the Army's few positions in the Chouf but have not yet really taken it on, partly because it has a lot more firepower at its disposal than the Phalangist militia.

The Army is positioned along the first ridge line of the mountains in a defensive posture, seeking primarily to protect the capital and control routes into it.

Some analysts here say Jumblatt and Syria may not agree to a cease-fire until the Druze militia first tries to gain a hold over the coastal road and access to Beirut's southern suburbs to strengthen its bargaining power with the central government.

This would bring the Druze militia and its leftist Lebanese and Palestinian allies into direct confrontation with the Lebanese Army and probably touch off far wider fighting.

Other analysts think Jumblatt may be content to oust the Phalangist militia from the Chouf and then sit down at the negotiating table to demand a bigger share of power in the government.

The original peace plan agreed upon in Paris in late August called for a meeting of Lebanon's 11 main ethnic and political leaders to hammer out a new power-sharing formula between Moslems and Christians and establish a new national unity government.

Official sources said today that Gemayel was ready to convoke such a conference as soon as a cease-fire took effect.