The debacle in Lebanon is a severe setback for US foreign policy. The reason does not lie in the intrinsic importance of Lebanon itself to the United States. The President, it is true, declared that it was a ''vital'' interest. But that was hyperbole: It is not. Instability in Lebanon is only a peripheral concern.
The damage arises from the way the issue was mishandled. Reagan's goal of creating a stable, unified Lebanon, free of all foreign forces, was ambitious, in view of the turmoil there since 1975. The administration's pursuit of that goal was fatally flawed.
1. It conceded too much to Israel. One purpose of Israel's invasion in June 1982 was to impose a peace settlement on a Lebanon dominated by the Maronite Christians under Bashir Gemayel and allied with Israel - incompatible with Reagan's goal. Yet the May 1983 agreement for Israeli withdrawal, brokered by Secretary of State George P. Shultz, gave Israel many benefits it wanted. It ended the war, created liaison offices for diplomatic relations, called for normalizing relations, and provided for joint Israeli-Lebanese patrols; and implicitly assumed a security role for Maj. Saad Haddad, Israel's ally. Finally, Israeli withdrawal was to depend on that of Syria. Then in December the administration announced ''strategic cooperation'' with Israel, to the dismay of friendly Arab states.
2. The US committed itself too tightly to the regime of Gemayel, a Maronite Phalangist. For a viable Lebanon, the Maronites, who have enjoyed predominance under the power-sharing agreement of 1943 but are now less than 30 percent of the population, will have to yield power to the more numerous Muslims - which they have resisted. Thus these sects saw US support for Gemayel as hostile intervention, delaying Maronite concessions. And Shultz's pressure on Gemayel not to cancel the May 17 agreement, as demanded by the Muslims and Syria, also worsened his position.
3. The US has been inept in dealing with Syria, which has been difficult. Syria obviously wishes to minimize Israeli influence and enhance its own, both in Lebanon and in the Middle East. Thus it was bound to reject the May 17 agreement, which it saw as another partial peace like Camp David, giving the Israelis special benefits. It also resented equating the withdrawal of Israel's invading forces with those of Syria, which had come by invitation in 1976. And viewing Syria as a Soviet puppet because of the massive Soviet military assistance was a distortion unhelpful to relations.
4. US policymaking has been confused and uncertain. The mission of the Marines was ill defined. On the same day recently, Shultz reaffirmed US support for the May 17 agreement, while the President said we had no position one way or the other. The secretary of the Navy said that naval gunfire was intended to support the Lebanese armed forces, only to be corrected by the White House and the Pentagon. Obviously, Secretary of State Shultz, Secretary of Defense Caspar W. Weinberger, and Robert McFarlane, a national security adviser, have favored different courses, and conflicts were often not settled by the President - raising the question: Who is in charge?
5. The administration has allowed preoccupation with Lebanon to deflect it from the pursuit of Reagan's initiative of September 1982 for a Palestinian settlement based on UN Resolution 242, which would serve US interests. That played into the hands of Israel, which had flatly rejected the Reagan plan, and was delighted to gain time in absorbing the occupied West Bank and Gaza.
Syria has skillfully exploited US mistakes for its own ends. As a result, it has won most of its negative goals: The May 17 accord is dead; Gemayel is at bay; the Marines are withdrawing; and the Lebanese Army is disintegrating under pressure from Muslim militias. Achieving its positive aims, however, will be harder than being a spoiler. Syria's interests will not be served by chaos. It may well prefer a stable Lebanon, albeit under Syrian influence, if only as a buffer against Israel. But to get it, Syria will have to deal with Israel's security concerns and cope with Lebanon's feuding sects and factions.
The US has paid a heavy price in terms of credibility among friendly Arab states and allies. A repetition would be disastrous. Yet it could happen on the Palestinian issue. On recent visits to Washington President Mubarak of Egypt and King Hussein of Jordan strongly urged the US to move for a settlement. That would serve US interests. But even if the Arabs could be induced to negotiate, a solution would require intense pressure on Israel. Unless Reagan is ready to do that in an election year he should not start down the road.