THERE IS AN unmistakable grimness to the negotiation that is to open today at Camp David between the foreign ministers of Egypt and Israel and Secretary of State Vance. Gone is the sense of high drama that beckoned as President Sadat and Prime Minister Begin began Camp David I with President Carter last fall. Gone, too, is the twin expectation that face-to-face negotiation between Israelis and Egyptians would supply the requisite political adrenalin, and that American resourcefulness would surely make up the shortfall. What remains is a cold awareness that the new form and pace of diplomacy, far from sparing the parties brutally difficult political decisions, makes them all the harder to avoid.

The "basic deadlock," Mr. Carter correctly says, is the relationship between an Israeli-Egyptian treaty and a comprehensive settlement. Egypt, under broad Arab pressure to serve the Palestinians, would condition its support for a Sinai pact on Israel's specific pledge to get cracking on a West Bank negotiation. The Begin government, under fierce internal strain, feels that to make such a pledge when there are no Palestinians (or Jordanians) yet ready to negotiate is to preclude a Sinai agreement altogether.

This question is not likely to be settled by the assembled foreign ministers. For one thing, Mr. Vance's two guests lack the authority to commit their respective governments. For another, Mr. Carter, by announcing his availability for a second summit, almost certainly assured that the political leaders would save the hardest parts for him. A two-part meeting is in store.

We would, however, underline one thing now. Since Camp David I, the Middle East has been seized by the revolution in Iran. If this has not, as Yasser Arafat exulted in Tehran, turned the region "upside down," then it has deeply affected Cairo and Jerusalem. Egypt has felt harder pressed to demonstrate its Palestinian loyalties. Israel's anxieties about dealing with a regime vulnerable to a similar Islamic tide have increased.

Yet Mr. Carter is right in saying that events in Iran make an Arab-Israeli peace even more urgent. The shah's fall has cost Israel its most loyal and valuable friend in the region, giving it new reason to take advantage of an opportunity to end the state of hostilities with its most formidable adversary -- an opportunity that it cannot expect to recur for years and years. The shah's fall warns Egypt to take the one step that will help it most to concentrate on its frightening internal tensions, even while leaving open for Cairo a role as the leading stabilizing power of the region. It would be unforgivable for either to suppose there could be a Camp David III.