Beirut — The Lebanese Army may make or break Lebanon's current grope for stability. If history repeats itself, it will break it.
The tri-nation force currently supervising the evacuation of Palestine Liberation Organization guerrillas is mandated to stay only 15 days after the last guerrilla leaves.
Those 15 days are set aside for helping the Lebanese Army take control of itself for the first time in six years.
The Army is distrusted by both Christians and Muslims. The Christians suspect the Muslim rank and file of collaborating with the Muslim leftist militias of west Beirut. Similarly, the Muslims have grave misgivings about the predominance of Christians in the officer corps, including the Commander in Chief Victor Khoury.
They accuse General Khoury and his officers of supporting the right-wing Christian militia of President-elect Bashir Gemayel.
Midway during the Israeli siege of west Beirut, American envoy Philip C. Habib suggested deploying the Lebanese Army in Beirut. Citizens in the war-ravaged capital chuckled. They knew the Army had neither the strengh nor the cohesiveness to do it.
But with Mr. Gemayel as president, the question of the Army takes on an entirely new light. The 34-year-old militia boss, known to have personally had a hand in some of the bloodiest civil war fighting, has promised to meld his 20, 000 men into the Army.
In the same breath he says he will offer the other militia groups the same chance to join up. If they don't, they will be disbanded.
Lebanon has seen Mr. Gemayel keep his word in such situations. After the civil war, Mr. Gemayel moved to consolidate the power of his Phalange militia as the Christian force.
In one day, his men mowed down approximately 300 members of the National Liberal militia. The party headquarters in Ain Saadeh, on the main mountain highway, is still in shambles after being blown up by the Phalange.
Sources in the militia explain it is purposely left unrepaired to remind people what competing with Mr. Gemayel's private army will bring.
The private army mixed in with the splintered Lebanese Army would make it a potent force - without equal once the Israelis withdraw.
The Lebanese Army numbers about 23,000 men. The Phalange would bring that figure up to 43,000. The difference would be that his men are well disciplined and experienced in the street fighting that has engulfed the capital for more than seven years.
Lebanese Army sources admit not all units are totally loyal. During the more than two months of battle between east and west Beirut factions last year, both the Muslim leftists and the Phalange had parts of the Army fighting with them. Other Army units merely got caught in the crossfire.
The ''new'' Army filled with Mr. Gemayel's men is unlikely to hesitate and look for confessional motives behind orders like the present Army often does, Lebanese political sources said.
The day before the PLO exodus began, the Nasserite militia Morabitoun held a parade - to show off new weaponry. The weapons - artillery guns, rocket lauchers , tanks - were gifts from the PLO.
The PLO and Syrian departure leaves their ally the National Movement in the lurch.
Even with the new weapons, the National Movement is vastly outnumbered by the Phalange alone - not to mention by the Phalange combined with the Army.
The leader of the National Movement, Druze chieftain Walid Jumblatt, saw the writing on the wall when the Israelis encircled west Beirut.
In late June, Mr. Jumblatt said the leftists were finished. ''We will have to find new ways of struggle.''
When Mr. Gemayel was elected, Mr. Jumblatt said ''Lebanon has become one big prison.''