THE MIDDLE EAST is in an unusual stage in which almost all the parties are talking, at least, about peace. This guarantees nothing, but it represents a welcome change from the recent violence. It represents, too, a success and a responsibility for American diplomacy. The United States' ideas are the center of the discussion, and its influence is the prize that every other party hopes to bring to bear in its fashion.

In Lebanon, the question is how to peel off the foreign armies and create a situation stable enough so that they won't come back. The obvious answer is to build up the Lebanese government, but that can only be done in stages. Meanwhile, the Israelis want security in southern Lebanon to be assured mostly by their own cooperation with the Lebanese. That sounds reasonable, but it cannot be allowed to mean simply that the Israelis will enable their client, Maj. Haddad, and some Christian militias to ignore the authority of Beirut.

The Israelis are helping to keep the peace among Lebanese in the areas they occupy. They must shift that burden to others -- to Lebanese and perhaps to international representatives -- and not use "peacekeeping" to cloak a semi-permanent occupation. Lebanon's new president, Amin Gemayel, will offer his ideas on how to do this in Washington this week. Is not Syria ready to make suggestions, too?

Meanwhile, nothing can be allowed to draw attention or energy away from the central subject, President Reagan's peace proposals of Sept. 1. In Amman, King Hussein and Yasser Arafat presumably have been conferring on the Reagan suggestion for a negotiation to establish Palestinian self-rule in part of the West Bank "in association with Jordan." The explanations and evasions that came out of Amman attested mainly to their reluctance to say no, and to the difficulty of their saying yes.

Do Jordan and the PLO realize there is no other conceivable way, without American sponsorship, to roll back Israel? At the least, they wish to position themselves to thrust the onus for failure, if it comes, on Israel. The Israeli government, by sticking to its settlements policy and by rejecting the Reagan initiative even as a basis for talks, makes that a tempting strategy. King Hussein and Mr. Arafat must understand, however, that it is a strategy for leaving Israel in occupation of Arab land.

In presenting his proposals on the Palestinian question, Mr. Reagan made sure to detach them from his commitment to Lebanon. This was wise. Lebanon is going to be sticky. The Palestinian issue is the continuing priority. The United States remains under an unrelenting obligation to keep up the drive Mr. Reagan began on Sept. 1.