Gemayel's two remaining cards

The latest negotiating setback over Lebanon - and the fighting that has automatically followed - suggest the showdown between nominal Lebanese President Amin Gemayel and neighboring Syria may be a bit less one-sided than initially assumed.

A bit.

Sooner or later, Syria seems likely to win its objective of an uncontested central voice in Lebanese politics - and the removal of the Americans and their West European allies from the fray. Sooner remains far more probable than later.

The Syrians are sufficiently confident of this to have rejected the latest compromise proposal for entente with Mr. Gemayel. Damascus says its oft-repeated terms for a settlement remain unchanged: first and foremost, an unconditional scrapping by Gemayel of Lebanon's May 1983 peace accord with Israel.

But Gemayel retains at least two cards in his hand. They are not trumps, but even the far stronger Syria may not be able to ignore them altogether.

The first is the Lebanese presidency. True, it is an office virtually stripped of power on the ground. Gemayel's Syrian-backed opponents have nearly disintegrated his Army. They are poised to attack the hill town of Souk al Gharb , perched commandingly over Beirut and the nearby presidential palace at Baabda, about the only part of Lebanon that Gemayel still can claim to control. But a Gemayel resignation could fatally undermine the institution of the Lebanese presidency - especially if, as so far seems the case, a willing substitute president doesn't appear - and also undercut the precarious religious-political system by which Lebanon, however imperfectly, has been governed since the 1940s.

This, even by Lebanese standards, might mean chaos - in the form of unbridled bloodletting among rival Maronite Christian, Druze, and Shiite Muslim militiamen whom no outside power can totally control.

One of Syria's aims, throughout its direct military involvement in Lebanon from the final stage of the 1975-76 civil war there, has been to avoid this kind of free-for-all. Instead Syria has sought - and seeks - a balance of forces next door, with Syria at its fulcrum.

Gemayel's second ''card'' is the Phalangist Party - and more importantly a Phalangist militia that often has seemed answerable only to itself. The Phalangists and their militiamen, like Gemayel, belong to Lebanon's Maronite Christian community. In the old days, the Maronites ran Lebanon. Not so now, although some Western analysts suspect they may run Amin Gemayel.

Lebanon has, since the mid-1970s, been partitioned in everything but name. Increasingly, it seems evident that any stability must involve greatly diminished say for a Maronite community that, demographically, has been whittled down from slight majority to sizable minority.

Militarily, the Maronites are outgunned as never before. With only slight resistance, they have lost various key outposts - notably, last week, the coastal town of Damour, south of Beirut - to the Syrian-backed Druze and Shiites. And Israel has, of late, telegraphed a distinct disinterest in intervening on the behalf of their old Phalangist allies to redress the balance.

In a rare open acknowledgement of the turning tide, the Phalangist militia has announced that it is closing down its five outposts in southern Lebanon, where the population is mostly Shiite.

But rarely in their embattled history have the Maronites charted strategy merely on the basis of balance of forces. If apparently incapable of victory, the Phalange can make much violence. At the outset of these last two weeks of fighting, Phalangist militia chief Fady Frem alluded to this when calling his troops on alert.

''This is not the time to think, analyze, or anticipate,'' he began, in a statement broadcast by Phalangist radio. ''The enemies no longer want to win a (single) battle, but want a decisive and final battle in the war being launched to erase free, independent, and sovereign Lebanon from the map of the world.''

Gemayel's reluctance so far to bow completely to Syria's terms for entente may partly reflect a sense that not all cards are in Syria's hands. As for the Syrians, their strategy could become clearer during a visit to Damascus, starting Monday, by Saudi Crown Prince Abdullah.

Yet so far, Syria seems to have decided to wait out Gemayel - while its allies inside Lebanon hike their military pressure on him and his dwindling Army.

While Druze leader Walid Jumblatt takes the lead in demanding that Gemayel resign, Syria's silence on that point seems intended to drive home the point that the beleaguered President might best salvage what is left of his authority by making a deal with Damascus.

Syrian's - and its Lebanese allies' - care so far not to engage Israeli forces in the latest fighting suggests a similar message for Israel. The Jerusalem Post has explicitly called on the Israeli government to revert to the kind of pragmatic, indirect understanding with Syria over Lebanon sealed after the 1975-76 civil war there. Israel generally steered clear of involvement above a ''red line'' slightly north of the Israeli-Lebanese frontier, leaving law and order in most of Lebanon to the Syrians.

''It is time to recognize the situation in Lebanon for what it really is,'' the Post commented Monday, ''a power struggle between Israel and Syria over the inert body of a shattered and dismembered Lebanon. . . . Israel cannot therefore escape the reality of Syrian primacy in Lebanon.''

The Israelis, who invaded Lebanon in June 1982, remain in the southern part of the country. And Sunday, Israel resumed air strikes further north, targeting an area near Damour. Israeli officials have suggested the strikes were not intended as a prelude to intervention on the Phalangists' behalf near Beirut. Instead, the strikes are described as a warning to Damour's new Druze overlords that they cannot allow Palestinian or other anti-Israeli guerrillas to reinfiltrate closer to Israel's border.