The recent record of the Middle East suggests that things have a way of blowing apart just when the necessary elements for accommodation seem to be falling into place. Right now may be just such a moment, judging from talks with knowledgeable Western authorities who have been remarkably prescient in the past.

These analysts are even ready to identify the prime candidate for the spoiler's role: Ariel Sharon. Rough and ever-ready for military solutions to any and all Israeli security problems, the Israeli defense minister is not given to subtlety--his longing to invade Lebanon was advertised well in advance.

Right now, at least some experts believe, he may well be telegraphing another punch: an Israeli military sweep through Lebanon's Bekaa valley, designed to drive out the Syrian occupiers who provide the main means of support for the 8,000-plus Palestine Liberation Organization fighters still in Lebanon.

Before dismissing the idea as recklessly irrational, hear out the argument. The United States has a clear policy; it builds logically on Camp David's proposal to begin with a five-year period of "full autonomy" for the West Bank and Gaza Strip. The Reagan plan advances only in one respect; while foreclosing no ultimate solution, it states a U.S. preference for some sort of federation between the West Bank and Jordan.

Egypt's President Hosni Mubarak was in town last week glowing with optimism that all the Arab "moderates" (he includes among them PLO chairman Yasser Arafat) are deep- down in favor of the "Reagan initiative." Mubarak believes the PLO and Jordan are on the edge of meeting its key conditions--public recognition of Israel's right to exist and acceptance of the United Nations resolutions underpinning the Camp David accords.

All it would take for Jordan's King Hussein and Arafat to take the plunge off the high board, Mubarak argues, is some reassurance that there is water in the pool. That means some confidence that the United States, whose influence in any further "autonomy" negotiations would be crucial, is able and willing to exercise restraint on Israel. The litmus test is a demonstration that the United States can bring about Israel's withdrawal from Lebanon.

But the Begin government says it wants no part of the Reagan plan. What better way, then, to scuttle it than by digging in on the issue of withdrawing from Lebanon? In a matter of not too many months, the United States could be too incapacitated by the 1984 presidential campaign for the judicious practice of Middle East diplomacy.

The rub is that perpetuation of the status quo in Lebanon weighs heavily on Israel-- economically and politically. A low-level war of attrition is taking its weekly toll of Israeli casualties at the hands of PLO guerrillas.

Enter Sharon, the champion of the military quick fix with a record for pushing his instructions to the limit (and beyond)--and, recently, of carrying the Cabinet and Prime Minister Begin along with him. His distaste for the U.S. mediation role has already been demonstrated by his clumsy effort to destroy the work of U.S. special envoy Philip Habib by trying to cut a separate "normalization" of relations with Lebanese authorities.

Crushing the Syrian-PLO presence in Lebanon would suit Sharon's nature as well as his sense of what suits Israel's security. Israel would be in a position to dictate the pace of its own withdrawal. Given the likely uproar in the "moderate" Arab world, there would be no Camp David-Reagan music to face. Israel's de facto absorption of the West Bank could proceed.

For pretext, the new Soviet-supplied SAM sites in Syria or a "last-straw" ambush of an Israeli patrol in Lebanon would serve Sharon. Nothing more substantial was required for the original Lebanese invasion in June.

If the parallels are unsettling, the experience of Lebanon is also a deterrent. So is its impact on Ronald Reagan; he is angry enough to have signaled the preparation of contingency plans for using aid to Israel as leverage. It is not easy, moreover, to read the mind of Menachem Begin or to measure his mastery of his own defense minister. What you can be relatively certain of, however, is the general direction in which Sharon's instincts would lead him if allowed free play.