Gemayel's own Christian backers threaten to withdraw support

Lebanon is moving toward a decisive moment, as President Amin Gemayel struggles over his reply to a Saudi-mediated peace plan and the United States Marines prepare to finish their pullback.

A major hitch has delayed Mr. Gemayel's decision on the plan already approved by Syria: Right-wing Christian leaders have threatened to withdraw their support for him if he agrees to renounce the May 17 troop withdrawal agreement with Israel, one of the plan's provisions. This would cost the beleaguered leader his main power base.

Former President Camille Chamoun, chief of the Maronite Christian National Liberal Party, announced that he would withdraw confidence and cooperation from the regime and refuse to take part in any Cabinet or national reconciliation dialogue if the President scrapped the accord without alternative guarantees that Israeli and Syrian troops withdraw.

His son, Dany Chamoun, a potential presidential contender, said: ''The agreement is the only peaceful way to liberate south Lebanon (from Israeli control). The southerners have had enough tragedies. We do not want to turn south Lebanon into another Golan Heights.'' He referred to the Syrian territory occupied by Israel since 1967.

Christian leaders fear that, without an alternative to the May 17 accord, foreign forces will remain and the country will be de facto partitioned.

Fady Frem, leader of the Christian Phalangist ''Lebanese Forces'' militia, added an equally ominous threat by warning that his militia would turn against Gemayel if he yielded to ''Syrian pressure'' to repudiate the pact.

''If the President sees that the solution is in Damascus and he wants to come under Syrian control just to calm down the situation, you can be sure the Lebanese Forces will not go along,'' he said. He pledged to help form a new oppositon front to block the abrogation.

The impact of the new Christian resistance is best reflected in the fact that Gemayel is a former commander in the Lebanese Forces and was a member of the Phalange Politburo. The Phalangist Party - headed by his father, Pierre - has not made a formal statement on the plan. But it is widely reported that key members are deeply opposed to what they see as giving in to Syria.

If the main Christian parties do split over whether to accept the Saudi plan, Gemayel would have difficulty organizing a credible reconciliation conference to debate government reforms without all the traditional Christian leaders.

At issue is evening the balance of power between Lebanon's majority Muslims and minority Christians.

On Thursday, Gemayel met with his father and Camille Chamoun at the presidential palace in an attempt to gain their support for what may be Lebanon's last opportunity for peaceful resolution of the nine-year crisis. Saudi-appointed mediator Rafik Hariri also attended the meeting, then left for Damascus.

In west Beirut, Muslims charge that the President was deliberately dithering. The newspaper As Safir noted: ''At stake are matters bearing on the fate of the country, which cannot be dealt with through procrastination and attempts at improving (the administration's) negotiating position.''

The political impasse has not delayed movement at the Marine base at Beirut airport. Lt. Col. Charles Rinehart said the pullback to Sixth Fleet ships off Lebanon's shore was ahead of schedule.

Gen. James Joy, the Marine commander, said ''we are not in any type of panic operation.'' The Marines are expected to leave their base over the weekend in a single swift move so that no troops are left vulnerable.

General Joy added that there have been negotiations with the Muslim militias that surround the compound. ''We have assurances from the various factions that they do not intend to interfere with our orderly withdrawal.'' But other Marine sources said that there is deep concern about the possibility of an attack by extremists, designed in part to discredit the Muslim factions. They have restored calm to the west Beirut with the deployment of a Lebanese Army brigade sympathetic to the Shiite and Druze groups in place of militia gunmen.

The Marine base is beginning to look like a ghost town, with skeletal wood frames and floors left naked by large tents already packed away. This, along with furniture retrieved from the bombed US Embassy, will all be left behind. The mood at the base Thursday was one of anxiety and sadness.

The Israelis, meanwhile, reaffirmed their commitment to remain involved. For the third time in five days, Israeli jets bombed what a spokesman described as ''terrorist bases'' near Bhamdoun in the mountains near Beirut. Despite Israeli charges that Palestinian guerrillas are preparing to move into Beirut, Western sources say there is no physical evidence to prove the claim.

Shiite and Druze leaders say the Palestine Liberation Organization will not be allowed to return. Abu Musa, leader of the PLO rebellion against chairman Yasser Arafat, was quoted Thursday as saying the guerrillas ''have no desire to reestablish an armed presence in Beirut, nor do they have any intention to.''

He added: ''Our armed presence should be directed against our Israeli enemy.'' However, he said his branch of the movement was ready, if asked, to give any ''political or military assistance'' to its Lebanese allies.