Among those who regularly monitor the mood and the machinations of the Middle East--the political not-so- merry-go-round--there is once again that agonizing sense of an opportunity hanging out there like a brass ring, just barely within reach. If it is grasped, there would be at least the pacifying effect of positive process at work to resolve the region's tensions and hostilities. If it is missed, history tells us there may be a long passage before it works its way around again.

So there is a lot riding on the peacemaking efforts of U.S. special Mideast envoy Philip Habib in Lebanon; on the tugging and hauling among the Arabs over the larger Palestinian issues, and on the U.S. effort to bring Israeli Prime Minister Menachem Begin around to the point of at least considering the "Reagan initiative."

And right there lies the crux of the matter: in the eyes of the United States and of the so-called moderate Arabs, however they may waver, Ronald Reagan's peace plan is the brass ring. But in Israel's eyes, the plan put forward by the president last September is potentially "a serious danger" to Israeli security, a violation of the Camp David agreements, and a sellout to Jordan's King Hussein.

Now the Israelis are entitled to their judgment of what constitutes a threat to their security. But the argument goes nowhere when the terms of the Reagan proposal are misrepresented beyond recognition. It is idle to speculate on the outcome. But it is not idle --indeed it is urgently necessary--to remind ourselves of what Ronald Reagan did, and didn't, propose in his efforts to build upon the Camp David accords.

Just to begin with, he didn't insist on everything. He didn't "concede" or "give" or "award" the West Bank and the Gaza Strip to Jordan, as some of Israel's most faithful American followers would have us believe.

We have the word of a uniquely qualified authority, Jimmy Carter. He is not exactly a Reagan ally. Yet he was quick to confirm that the president's plan in no way violates the agreements that he witnessed and helped negotiate at Camp David.

What Ronald Reagan did in his September speech was (1) endorse Camp David and 2) add an expression of the U.S. government's preferences-- thereby exercising a right that the two other signatories, Israel and Egypt, have claimed for themselves and loudly exercised.

"Both Israel and Egypt have felt free to express openly their views as to what the outcome should be," the president said. "The United States has thus far . . . avoided public comment on the key issues," the president went on. "But it has become evident to me that some clearer sense of America's position . . . is necessary to encourage wider support for the peace process."

Accordingly, the president expressed a preference for "self-government by the Palestinians of the West Bank and Gaza in association with Jordan." He offered this as an alternative to a far more insistent Israeli claim to the West Bank and an Egyptian demand that it be converted into an independent Palestinian state. The president said the United States would support neither position, while leaving the outcome to "the give- and-take of negotiations."

So where are the grounds for the Begin government's flat rejection of such negotiations? When pressed, Israeli officials point to what was supposed to have been a confidential list of U.S. "talking points" elaborating on the Reagan proposal, together with an Israeli briefing paper responding point- by-point. While none of this has any standing until serious, formal negotiations begin, the burden of the Israeli complaint with these opening U.S. positions has mostly to do with what the Israelis think their worst effect meight be.

Thus a U.S. "talking paper" proposal which simply says that there will be no American support for Israeli control of the West Bank and Gaza is interpreted in the Israeli analysis as prejudicial to the final outcome because it "effectively promotes Jordanian sovereignty" over the West Bank and Gaza.

Much of the Israeli argument is, well, arguable. That's what negotiations would be all about--that's the brass ring. King Hussein, the Palestinians and their Saudi and Egyptian supporters have a heavy responsibility to do their share of the grasping. But they at least have done some tentative reaching by expressing varying degrees of interest.

The same cannot be said for the Israeli government. It has not merely rejected the Reagan plan. It is falsely fostering a perception of it as a non-negotiable final American position. For as long as there is this Israeli refusal to reach even just a little, there is little hope that the brass ring--the only opportunity in sight for a measure of stability in a region that has given us five wars in 35 years--will be grasped.