THE UPCOMING General Assembly vote on Israel's settlements in territories occupied in 1967 puts the United States in a by-now familiar Mideast place - uncomfortably, unavodeably but perhaps usefully in the middle. Arab sponsors of the resolution criticizing the settlements wish the United States to reaffirm on this vote a criticism that both this administration and the last have made before. Not to do so would be to advertise to Arabs and Israelis alike, to dismal diplomatic effect, that the Carter administration lacks the stomach to stand up under the pressure of Israel and its aroused American supporters.

Yet the administration is well aware that to go with the Arabs on this vote, in an Arab-dominated forum in which the Israelis have no chance to win fair and equal treatment, would farther antagonize the Israelis at a difficult moment when it is essential to ensure their cooperation on larger matters. Ever since Foreign Minister Moshe Dayan's visit last month, U.S. officials have known that the Begin government, risking political trouble at home to accommodate Washington, has quietly determined to plant no more civilian settlements - with their implication of defiance and staying on; instead, there are to be "military camps," which sound less permanent and menacing from a settlement viewpoint, and the people who live in them will be draftees. Americans also know that Prime Minister Menahem Begin, to demonstrate good faith on an issue of the utmost emotional and political content for him, has even called out the army to prevent right-wing civilian settlers from planting unauthorized settlements.

The American task on the settlements resolution, then, is to find a path consistent both with its condemnation of past Israeli policy and its awareness of the discreet changes Israel has now made. This must be done, furthermore, in a way that will not brake the truly remarkable, if largely unremarked, progress that has been made in bringing the parties toward the Geneva peace table.

For the Arabs have crossed a tremendous barrier: They, including the Palestinians - including the PLO - are now talking not about whether to sit face to face with the Israelis to negotiate binding peace treaties, but about which particular Palestinians will so sit. And the Israelis, led by no less "inflexible" a figure than Begin, have crossed a similarly impressive barrier: They are not arguing over whether to sit with Palestinians but over which part particular Palestinians.

The potential in these developments makes it all the more important for transient inconveniences like the General Assmebly resolution to be handled as smoothly as possible. The parties in the Mideast conflict have much more important business than to get caught up in maneuvering forpropaganda purposes at the U.N.