The talk is of a deepening involvement in Lebanon. "Is our Beirut strategy getting us in or out?" Even before we have finished debating whether Central America is "another Vietnam," we have taken up the same question in respect to the Middle East.

Fine. It is prudent to be wary about Lebanon, a humbling place that has repeatedly brought its friends--not to speak of its citizens--to grief. The immediate American mission, to halt the slide toward full-scale civil war and partition, may be unachievable. A desperate Ronald Reagan, bent on salvaging both American credibility and his own prestige, may up the military ante beyond the limits of public tolerance and sound policy alike.

Being prudent, however, is different from being panicky. Spiraling frustration is not the only course open in Lebanon, and going crazy is not the only choice for Reagan.

What is most striking about American policy in Lebanon is its divergence from what the president's approach elsewhere might lead one to expect.

Though Syria stands behind the Beirut government's local challengers, and the Soviet Union behind Syria, Reagan has so far kept within bounds the element of East-West proxy conflict that looms so large in his policy in Central America. This is a matter of some unease to the Gemayel government, which has seen its challengers' Syrian connection as its best ticket to greater American support, and to the Israeli government as well.

Instead, Reagan is encouraging "national reconciliation" among the Lebanese. Think of it: he is trying to induce the government we support to negotiate a sharing of power with its rivals. He is not saying, as in El Salvador, that the government is the government and those opposing it should join its elections or be hunted down. His concern for the international aspect is evident, but he seems to recognize that the Lebanese agony originates in an internal political conflict.

Whether the administration has yet got the right balance between the military and the political, the international and the internal, is far from assured. The ever-jittery Saudis, not alone, are openly anxious lest the American military role become too strong.

All the same, the accent on internal reconciliation constitutes a real intellectual and policy breakthrough. Reagan may yet be faulted for attempting a fool's errand or for intervening in another nation's internal politics. But, presumably, the United States does not intend to dictate which of the 17 communities gets what share of political power, just to help hold the ring.

In Lebanon, furthermore--here's another divergence from Central America-- the president recognizes more fully the value of hitching American policy to that of other leading friendly countries of the region. The Saudis are the Mexicans of the Middle East: important, self-directed, difficult to work with and count on but essential to any policy's success.

Lebanon's record of fratricide and its vulnerability to foreign manipulation make everyone wonder if it can ever again act like a single nation. Surely it's worth something, however, that serious Lebanese still believe the effort to be worth making. At the moment the Lebanese communities may be in what Arab League ambassador Clovis Maksoud calls a survivalist frame of mind, one that works against collectivity. But the residual feeling of being Lebanese is there.

There is, furthermore, Maksoud testifies, a consensus in the Arab world--a world that tends to operate by consensus--on what a fair Lebanese settlement might be: Christians would be preeminent but not dominant, and other groups would have a political and economic stake in the country's unity. Between such a consensus and its realization lie many heartbreaks--many more deaths. A premature surrender to despair, however, would be a cruel blow to the Lebanese.

Ambassador Ghassan Tueni, a Lebanese with a sense of his country's tragedy, offered these observations in Washington the other morning. The war, he said, is "a war of impossible victories"--no group that wins it can achieve its political aims--and at the same time "a war of impossible defeats"--no group can be expected to accept defeat. "The solution," he said, "is to embark on the solution": to deepen an internal dialogue that will go on, raggedly, for years.

I think it is worthy, necessary and feasible for the United States, which professes to have major interests in the Middle East and to be a world power, to try to help Lebanon make a fresh start. Poor Lebanon is, I keep thinking, an unoffending country whose sins have all been committed against itself.