HOW DID MR. CARTER sidle up to publicly inviting Mr. Begin to Camp David without being sure he would come? Why did he not also invite Mr. Sadat? Why did Mr. Begin refuse the invitation? Since the facts have not yet been fully liberated, we hesitate to assay the exct mix of pride, confusion and purpose in this sequence. It is clear only that the search for a peace treaty between Egypt and Israel is in a state of extraordinary fragility. Mr. Carter saved the Mideast negotiations, at least temporarily, by issuing a second invitation to Mr. Begin, this one for "frank discussions" with himself. Then, presumably, negotiations will follow at Camp David with Mr. Khalil "or" President Sadat. Egypt and Israel are lurching toward the moment when they must decide whether peace is really for them.

Is it? At Camp David II last week, there was apparently no substantive progress on the issues. Optimists might say that one reason lay in the fact that neither Mr. Sadat nor Mr. Begin was there. Pessimists would respond that the collection of geopolitical changes and perceptions summed up in the word "Iran" has put a crushing terminal burden on a process that was sagging dangerously anyway. The Egyptians have wondered all along if Israel could take the risks of peace. The Israelis fear now that Egypt finds peace less appealing than a return to the Arab family and a new role as the United States' favorite regional surrogate. President Carter, still the optimist, believes that political leadership can jump the historical, emotional and geopolitical gaps. We share his conviction that the gamble is worth taking.

Now as always, there is one root problem: the Palestinians. Egypt must show its fellow Arabs it is moving toward a Palestinian political solution. The Israeli government -- any government -- must show its citizens it is not losing control and creating a menace to the Jewish state. This is the basis of the argument over whether the link between an Egyptian-Israeli treaty and the onset of Palestinian "autonomy" should be tight, as Egypt demands, or loose, as Israel insists. A compromise is, we believe, possible, perhaps with a first mutual good-faith demonstration in Gaza. But both sides must accept that neither can get the full measure of assurance it desires. In the inflamed conditions of the Mideast, nothing is harder than to settle for something not as certain as you wish -- and nothing is more necessary.