PROBABLY THE Israeli invaders of Lebanon will soon have accomplished their declared purpose of removing Palestinian artillery from the border zone. A Syrian decision to join the war could spoil this prospect, but otherwise superior Israeli power will tell. Israel will then be faced with the question that has sooner or later soured its every victory: how can military coin be exchanged for peace?

In this case, the answer is easy. Israel is relieving the sort of border threat that no nation with the choice would abide. It is doing so, regrettably, not only by striking PLO forces but also by dealing death and injury to a great many Lebanese and Palestinian civilians who found themselves in the way of the war. If the past is any precedent, PLO guns will be back in action firing at the Israelis from the next hill -- there is always a next hill. No Lebanese government structure exists to expel the foreign forces -- Palestinian and Syrian as well as Lebanese -- which mock Lebanon's sovereignty. It still seems too optimistic to assume the rising disgust of many Lebanese with the Syrians and PLO can provide an opening for a new political combination.

In this dismal context, the Security Council's resolution may offer at least a flimsy basis for restoring superficial calm. (Don't dismiss superficial calm; it's preferable to deepening violence.) The council demanded 1)that Israel withdraw at once and "unconditionally" and 2)that "all parties" (the PLO) halt "immediately and simultaneously all military actions within Lebanon and across the Lebanese-Israeli border." In brief, both parties have responsibilities. The task of diplomacy is to sort them out.

Nothing that happens in Lebanon, however, is going to put Lebanon back together again. Its distress arises in good measure from the Israeli-Palestinian conflict, which arises in turn from the two parties' failure to respect each other's claims to nationhood. At Camp David, Israel promised to enter a process in which Palestinians could bring to a table their claims to a West Bank-Gaza state. Tragically, the PLO decided not to test that process. Equally tragically, the Begin government has sought to ensure that no Palestinians of substance would change their mind.

Israel's determination to police its northern border cannot be faulted, at least in theory, and certainly not by those who urge Israel to take the risks that "full autonomy" on the West Bank would entail. But its apparent repudiation of its Camp David pledge to consider change on its eastern border is unforgivable. That brings everyone back to Camp David -- frail but representing the only existing or conceivable common ground, Israel's best hope, and the Palestinians' -- and Lebanon's.