WHY, ASKS SENATE Foreign Relations Chairman Frank Church, is the promise of Camp David fading? His answer is simplistic and unhelpful. He locates two villains. One is the State Department, whose so-far-unsuccessful efforts to draw Jordan and some Palestinians into the peace process he criticizes as a departure form Camp David. In fact, such efforts, properly conducted, are not just essential to give Egypt the cover, if not the company, it needs to make peace with Israel first -- they are central to the spirit, if not the precise letter, of Camp David.

The senator's second villain is Saudi Arabia, whose failure to support Egypt he would punish by reviewing the whole American-Saudilink, including the sale of F15s. He overlooks that the Saudis, on whom the United States increasingly depends for oil, seem already to be reviewing their ties to Washington. That the United States can dictate policy to them is a fiction -- a dangerous one. The same may be said for the assumption that the Saudis have nobody to turn to, if the United States cancels the F15 deal; there is always France, and now at least the possibility of the Russians, as well. For Moscow, responding to the Saudi ambivalence, is extending feelers to the heretofore fiercely anti-communist, anti-Soviet Saudi monarchy. How would Sen. Church deal with that?

The execution of American policy since Camp David has hardly been flawless. Sen. Church's point that the administration leaned too publicly to the Egyptian side in exchanges last December is one we made at the time. Nor would we argue that the administration should be spared congressional criticism, which is likely to flow more copiously now that the Camp David honeymoon, which coincided with a congressional recess, has ended. The Church pronouncement, given to a B'nai B'rith audience, was a warning that Israel's American Jewish constituency intends to weigh in heavily as the negotiations go down to the wire. That the negotiations are so delicately poised, however, is precisely why criticism must be constructive and fair.

Why, then, is the promise of Camp David fading? Any comprehensive listing would have to include Syria's and Iraq's determination to "unify." A hoot of derision was heard last October when those long-time rivals, to counter Egypt's quest for a "separate peace," undertook an exercise in "unity" that Arab nations have tried to no lasting effect a dozen times before. Today there is a grudging respect for their seriousness. The possibility of defense cooperation, including the stationing of Iraqi units on the Golan Heights, is not dismissed. The Syrian-Iraqi opening has contributed significantly to the pressures that, to the administration's keen disappointment, have pulled the Saudis into anti-Camp David harness. The Saudis murmur that they cannot accommodate U.S. diplomacy in the Mideast and U.S. oil requirements at the same time.

Behind all these Arabs moves is, of course, Iran, which is making not only Saudi Arabia but Egypt itself worry about investing too much confidence in American diplomacy. The Egyptians have reacted by hardening their determination to show they will not make a separate peace. They are insisting on a timetable, of an explicitness not anticipated at Camp David, linking a Sinai pact and the onset of West Bank self-rule. The Israelis are reacting in a similarly defensive fashion, seeking harder guarantees against a change of heart or regime in Cairo, against a Sinaioil cutoff, and so on.

The other day a State Department envoy returned from Egypt and Israel, having failed to break their impasse. That revived talk of a second summit. Mr. Carter then set what an aide called a "precondition" -- so far unmet -- of mutual indications of flexibility. Figuring out how it can best be met -- presumably by another effort at the foreign ministers' level -- is the immediate task before American diplomacy. Events in the area, not to speak of Chairman Church's shot across the bow, underline the seriousness of the Israeli foreign minister's recent warning that Camp David could become "just another file."