Lebanese unity: more elusive without Pierre Gemayel?

The immediate impact of the passing of Pierre Gemayel, for 50 years a powerful figure in Lebanese politics, is that the nation's carefully constructed ''national unity'' Cabinet is knocked out of balance.

A replacement will have to be found speedily in order to restore the Cabinet's political and sectarian balance, and that may not prove to be an easy task.

Less visibly, but probably more important, Mr. Gemayel's death is expected by Christian sources to complicate the mission of his only surviving son, Amin, now President of the republic.

As a founder and leader of the 48-year-old Maronite Christian Phalange Party, Pierre Gemayel had the authority and prestige to secure Phalangist support for the President's current efforts to promote a Syrian-influenced peace process in the country.

That process is vehemently opposed by the right-wing Christian militia known as the ''Lebanese Forces,'' which has its roots in the Phalangist Party but retains a strong relationship with Israel. In recent years it has increasingly taken on a political identity distinct from the parent party.

The Forces were the brainchild and vehicle to power of Amin Gemayel's younger brother, Bashir, who was assassinated two years ago shortly after being elected to the presidency of the republic.

In the Forces' heyday under Bashir, the distinction between party and militia was slight, because Bashir's powerful personality and military muscle allowed him to dominate party policy.

Since Bashir's death, however, President Amin Gemayel has had to rely heavily on his father to restrain the growing tendency of the Forces to go their own way. Forces officials have never disguised their lack of enthusiasm for Amin - who was often at odds with his late brother, Bashir - and their suspicions that he has all along been preparing to cut a deal with the Syrians.

Now that Pierre Gemayel is gone, Christian sources fear it may prove more difficult for President Gemayel to secure the cooperation of the militia in plans to pacify the country. The Forces commander, Fadi Frem, recently stipulated three major conditions for acquiescence in the next phase of the government's security plan. His earlier reservations about the plan to deploy Lebanese Army soldiers in Beirut were overcome only after intervention by Pierre Gemayel.

The sources expected Gemayel's death to have the general effect of weakening the party's political strength, both in its relationship with the Forces and within the Christian community in general. At the same time, it is expected to sharpen a struggle for power which has already been quietly shaping up behind the scenes in recent months.

As President of the republic, Amin Gemayel was not free to assume the party leadership, which has instead gone to the relatively unknown Elie Kerameh. (Pierre had announced recently that in the event of his death, Dr. Keramah, a party stalwart and Gemayel's personal physician, would assume party leadership.)

But Christian sources say that since spring, Amin Gemayel has been building up his own Phalangist militia as a counterbalance to the Forces, which supposedly unite all the right-wing Christian military forces under one banner.

Amin Gemayel's recent reconciliation with the north Lebanese Maronite strong man, former President Suleiman Franjieh, was also seen partly as an effort to strengthen his own position within the Christian camp.

Pierre Gemayel survived numerous assassination attempts over the years. His passing signals the beginning of the end of an era that has been dominated by the sectarian godfathers who, now well into their 70s and 80s, continue to call the shots in Lebanon.