A high stack of American chips rests on the outcome of the battle at Suq al Gharb, the mountain town south of Beirut where the Lebanese army is making a stand against Druze and Palestinian units backed by Syria. On Monday, the United States broke through to a new level of commitment --and risk--by using American warships to come to the direct support not of the American Marines but of the embattled Lebanese army. Will the new show of force keep that army fighting, give pause to the hostile militias and their Syrian sponsors, and bring an early cease-fire? Or will the Lebanese army, the government of Amin Gemayel and the American position in Lebanon, in that order, collapse?

We will not attempt to predict the outcome, which could come at any moment. But it is worth observing that the single reason the outcome has remained unclear for so long is that the much abused Lebanese army remains in the field. The army has turned out to be neither the corrupt tool of the right-wing Christian Phalange, as some expected, nor the ineffective reflection of the country's internal strife, as others had thought. It is ethnically diverse, increasingly professional, and demonstrably prepared to take casualties in the service of the duly elected (by all communities) president. If it does not prevail at Suq al Gharb, the fault will not be its own.

It is asked whether the United States can "prop up" a government if it cannot get the support of its own people, and the answer is obviously no. The army, however, and the government are imperfect but working national Lebanese institutions. The problem is not so much that they are factional as that they are weak. Therein lies the purpose of the support being rendered by the multinational force. The idea is to exnd the existing narrow core of national sentiment and cohesion. But this prospect will be cut off if a cease-fire cannot be arranged soon and the focus turned to Amin Gemayel's promised new discussions on reapportioning Lebanese political power and rewards.

The passions separating the Lebanese communities are awesome. But the real issue is likely to be whether Syria now sees it in its interest to move to a political phase. It is difficult for the United States to say all of this, but it is true: the Syrians have effectively destroyed the American-sponsored Israeli- Lebanese agreement. They are forcing a redrawing of the political map in Lebanon. Rebounding from their disgrace of a year ago, they are recognized everywhere as a power in the region. The question is whether Syria will press its advantage and leave Lebanon without even a shred of hope to creep from the ruins. The answer will come at Suq al Gharb.