Gemayel faces defeat

Beirut is rapidly slipping away, despite major support from the United States. President Amin Gemayel's Army has suffered major defeats. More than half his men have switched sides or defected. His capital is surrounded.

In a perhaps desperate last ditch effort to regain some influence with his Muslim and Druze opponents, President Gemayel at time of writing Wednesday night was expected to open the way for abrogation of the Lebanon-Israel troop withdrawal agreement and call for further peace talks in Geneva. But concessions now may well be too late and too little to salvage his presidency.

A drive from Beirut to the coastal town of Khalde reflects the dimensions of the defeat facing the Gemayel government. As a prominent local politician commented:

''He is acting as if he is blind, because he certainly does not know what is happening around him.''

The six-mile stretch of road was abandoned except for a few militiamen whizzing back and forth in Lebanese Army vehicles either captured or turned over by defectors Tuesday. The highway is deeply pocked from shells and rockets and mortars.

The Lebanese Army was here in Khalde until 4 p.m. Tuesday. This was its front-line position on the outskirts of Muslim-dominated west Beirut. But Gemayel's army was beaten back, leaving the capital totally surrounded by opposition forces who had pushed all the way through to the Mediterranean Sea.

One of the checkpoints here is jointly run by Druze militiamen, who have been fighting the Army in the surrounding Shouf mountains since last September, and Shiite Muslim Amal gunmen, who won control of west Beirut last week. This symbolized what the government had feared most: the Druze and the Shiite militias, the two main opposition armies, have hooked up and are now operating together.

The first three miles is under the control of Amal. At their first checkpoint , the air was so festive that they had brought out their children to help celebrate. A slightly perplexed Ali Husseini, 1 1/2 years old, had been decked out in an oversized Army helmet, military belt, and was holding a toy rifle, an Amal emblem tied around his neck.

The position is directly across from the international airport and the US Marine complex. Even the Marines acknowledged the Amal conquest of the territory surrounding them, renaming Beirut airstrip ''Berri Airport,'' after Amal leader Nabih Berri. In another symbolic scene, US helicopters constantly ferried Marine supplies back to the ships offshore, in preparation for an eventual withdrawal after 17 difficult months in Lebanon.

From the Khalde junction south, the next three miles are held by Druze fighters from Walid Jumblatt's Progressive Socialist Party (PSP). They managed to reach the sea, after clearing a corridor of villages held by the Army and the Christian Phalange militia in an 18-hour campaign. It was the second, and perhaps fatal, blow to the Lebanese Army in the past 10 days.

Military sources confirm that 60 percent of the Army's combat-ready troops have defected or returned to their barracks, unwilling to fight. They also acknowledge that the opposition has taken 60 tanks, armored cars, or military vehicles, as well as a still uncounted but ''enormous'' quantity of arms and ammunition.

One of the sites now under Druze control is the Lebanon Beach Hotel, a gleaming white complex on the Mediterranean. It was here that Israel and Lebanon , after five months of arduous negotiations under US sponsorship, sat down at a table last year to initial an agreement on withdrawal of foreign forces from Lebanon. This was the pact that infuriated Muslims because it allowed a residual Israeli military presence and kept channels open for eventual normalization of diplomatic relations between Israel and an Arab state.

At time of writing, it was widely anticipated that President Gemayel would open the way for abrogation of the agreement as a condition for peace between his Christian-dominated regime and the nations Muslim majority. In a speech, scheduled late Wednesday, he was also expected to:

* Officially request the United Nations to replace the four-nation peacekeeping force in Beirut.

* Recall the remainder of the Lebanese Army to their barracks to prevent further bloodshed, and ensure that a cease-fire is maintained.

* Outline a 28-point package of reforms for discussion at a reconvened national reconciliation conference in Geneva Feb. 27.

Government officials were predicting the ''historic decision'' would lead to a breakthrough domestically. They conceded, however, that it would leave a void on the major regional issue of a pullout by the estimated 70,000 Israeli, Syrian , and Palestinian troops now occupying 80 percent of the country.

In preparation for the concessions, President Gemayel went to Zegharta in northern Lebanon Tuesday for talks with an old family and political rival, former President Suleiman Franjieh. Mr. Franjieh then traveled to Damascus on Wednesday to determine whether Gemayel's terms were sufficient in the eyes of the Syrians and Mr. Jumblatt to end the crisis.

But at a press conference in Syria, Druze leader Jumblatt insisted that, ''Amin Gemayel has to step down. There will never be any talks, any dialogue, any reconciliation with the Phalange or Amin Gemayel while he is in power.''

Mr. Jumblatt is now in a position to carry through with his threat. In Khalde Druze fighter Suhail Hamdan predicted that the joint Druze-Amal forces could march through the Shouf within the next week and take Souk al Gharb, the strategic mountain town that serves as the gateway to east Beirut.

As he spoke, the USS New Jersey loomed off the coast. But the Druze are not frightened by it or its ''flying Volkswagens'' - a local reference to the size of its one-ton shells.

Although US officials said during the Shouf war, that they would not allow the fall of Souk al Gharb, there now appears to be little they can do to prevent it.