MR. VANCE'S BAPTISMAL trip to the Mideast produced interesting evidence that "moderate" Arab states are hunting for ways to bring the Palestinians to the Geneva peace table. Just as the Secretary of State arrived in Damascus, for instance, it was reported that Syria was imposing tight new political and military curbs on the independence of the Palestine Liberation Organization -- a move foreshadowed, to be sure, by Syria's decimation of PLO forces in the Lebanese war last year. Egypt's President Sadat substantially clarified his earlier proposal that the PLO somehow federate with Jordan even before the Geneva conference reconvenes; this meets partway Israel's demand that the Palestinian question be treated within the context of a negotiation with King Hussein. The King himself indicated that, while he will not reach out for the role of representing Palestinians, which his fellow Arabs took from him at Rabat in 1974, he would receive back whatever part of that role is now offered to him. Saudi Arabia, whose oil riches and new self-confidence are making it increasingly the dominant Arab power, seems to using its influence to encourage the PLO's principal policy-making group, the Palestine National Council, to soften its stand on Israel at the Council's meeting in Cairo next month.

Taken together, these moves and hints of moves do not demonstrate that the PLO or its leadership or its membership are finally prepared to live side by side with Israel in peace. There is too much history and passion, too much illusion and irresponsibility, to support any such conclusion now. What these signs do indicate, however, is a welcome measure or acknowledgement on the part of concerned Arab states that the PLO''s aims and operations must be reduced to acceptable dimensions. The signs indicate, in a word, that the Arab states are in earnest about peace: they have better things to do than to spin out the fantasies of Palestinians who wish to undo Israel. That these same states were largely responsible for creating and sustaining these fantasies over so many years only underlines the importance of what they are doing now.

Mr. Vance, conducting a new administration's reconaissance, seems to have spent most of his time listening. He did inject one new American note, however, by hoping that the PLO, at its March meeting, modify the part of its charter denying Israel's right to exist as a state. Whether the PLO leadership, even if it is so inclined, can carry such a change is problematical. But there is no doubt that the change is crucial.The Israelis desire and deserve more than new words: they want new deeds expressing neighborly confidence. But the words are what one expects first.

Former Secretary of State Kissinger, to secure Israel's assent to the 1975 disengagement accord, promised Israel that the United States would not "recognize or negotiate with the PLO so long as the PLO does not recognize Israel's right to exist and does not accept Security Council resolutions 242 and 338." Saudi Arabia, for one, urged Mr. Vance to break this pledge and to move now toward American recognition of the PLO in order to put pressure on the Israelis to follow suit. But Mr. Vance seems to have made clear that the Carter administration will not open its Mideast diplomacy with a demonstration that the United States, if pressed, will go back on its word. In truth, if he wants to accomplish anything in the Mideast, he could not have done otherwise.

Meanwhile, the need grows for Israel to do what it can to make possible the further taming of the Palestinians. What will be more effective, a tough line or a softer one? Israel's politics and its people's anxieties so far have dictated the former. It is a real question, however, if the time for a crossover is not near. At some point, the Israelis must show -- specifically by accepting Palestinians as a negotiating partner and by indicating the territory they intend to exchange for peace -- that they are serious. A redrafting of the PLO charter to demonstrate the Palestinians' commitment to coexistence would put Israel on the spot where it would have to choose. For ultimately the Palestinian question is the Israeli question, too.