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.