PRESIDENT CARTER got in an unnecessary dig at the Israelis yesterday. From criticizing (reasonably, in out view) Israel's cramped statement on its West Bank intentions, he swept on (unreasonably, in our view) to criticize Israel's response to the Egyptian peace plan broadcast on Cairo Radio. He protested that Israel had "rejected" a plan that had "not yet even been made."

But if Israel is to be rebuked for reacting unconventionally and prematurely to a proposal not yet finally drafted and formally presented, should not Egypt be rebuked for unconventionally and prematurely floating such a proposal on Cairo Radio? Mr. Carter's competence as a mediator rests, precariously, on a common perception of his fairness. At a moment when the Israelis are feeling extraordinarily bruised, he cannot afford to put them off further by ill-timed remarks suggesting that he is choosing sides.

In fact, the Egyptian plan, to judge by Cairo's sketchy accounts, is an odd creature. It calls upon the Israelis to yield the West Bank (to Jordan) and Gaza (to Egypt) in advance of negotiations - over security arrangements. This is absurd at face and offered reason enough for Israel to speak up promptly and warn Egypt to polish its terms before the opening of the new phase in Mideast diplomacy marked by the forthcoming Mondale-Vance trip to the region. Obviously, Israel cannot surrender its high card, the territory, before negotiations even resume.

At the same time, the Egyptian plan has elements that, if refined by negotiation, could prove attractive to Israel. We refer to the suggestion that, as an interim measure, the West Bank and Gaza be turned over not to Palestinians but to Arab sovereign states. Does this not meet part way Israel's refusal to countenance establishment of a Palestinian entity on its frontiers?

At this muddy point, with both Anwar Sadat and Menachem Begin in evident political distress, the prime requirement to get negotiations back on the track. That is precisly the Mondale-Vance purpose. It helps to have an Egyptian proposal finally being prepared. It would help even more if the parties could find their way back to negotiating at a table, and not just by political speeches, radio broadcasts and Cabinet statements. The Arab-Israeli dialogue was bound to be rougher than would be any conducted parties more accustomed to talking with each other. Lately it has been getting out of hand. We cannot believe that close and quiet diplomacy would not induce positive changes in the positions of both sides.