You have to cover any assessment of the outlook in the Middle East with large assumptions. But let's assume, anyway, that Israel's Prime Minister Menachem Begin can keep his Air Force grounded for a decent interval. Let's presuppose, as well, that President Reagan can be persuaded to keep as quiet, say, as his special envoy, Philip Habib.

Then, barring the unexpected from some other quarter (another necessary assumption), it is possible to find a tiny ray of hope for a peaceful resolution of the Syrian missile crisis: it lies in an emergency committee of foreign ministers of four Arab League members (saudi Arabia, Syria, Lebanon and Kuwait), which was holding its first meeting in Beit ed dine, Lebanon, on June 7 even as Israeli jet bombers were on their way to Baghdad to destroy the Iraqi nuclear facility. The hope is presented by the fact, largely obscured by the uproar over the Israeli air raid, that these Arab mediators have scheduled a second meeting today in the Saudi Arabian capital of Riyadh -- and, if all goes well, a third meeting in Lebanon on July 4.

In short, a modest and not altogether unpromising peacemaking process seems to have survived the shock waves of Israeli nuclear non-proliferation, as practiced on Iraq. The initial public reaction from Arab capitals appeared to write off the Habib mission as "futile" (Syria) or "irrelevant" (Saudi Arabia). American influence, it was widely surmised, was sorely compromised by the use of American aircraft in the raid and the permissiveness, in Arab eyes, of President Reagan's press conference remarks that Israeli leaders "might have sincerely believed it was a defensive move."

Begin wsted no time seizing on the president's words for electioneering purposes, while loudly threatening to loose his planes against the Syrian missiles in Lebanon if Habib didn't produce an answer to Israel's liking, fast.

But even as Saudi Arabia's foreign minister, Prince Saud, was pronouncing the prospects "bleak" for the Habib effort, Saudi officials were drawing pointed attention to the meetings still scheduled by the Arab League foreign ministers.

Their merit, at this tense moment in Arab-American relations, is that while they are critical to the Habib shuttle (and could even be called a calculated byproduct), they are essentially an Arab initiative.

The point of this Arab exercise is not to settle the Syrian missile crisis -- that will require Israel agreement. What the Arab League mediators are trying to do is to put back together the Humpty Dumpty that passes for a central government in Lebanon.

"We are going back to square one," says one Saudi official who is familiar with the basic strategy.

This means, first of all, attempting to arrange a cease-fire between all the warring factins and forces that over the years have turned Lebanon into a bloody and ungovernable battleground. This is a tall enough order when you consider that, in addition to a largely ineffectual United Nations contingent, the Syrian occupiers in the name of an Arab League "deterrence" force, and the guerrillas of the Palestine Liberation Organization, there are a half-dozen Lebanese factions -- Christian and Moslem -- Left and Right, all having at one another in the name of either peacekeeping or power-grabbing.

The Arab League talks of creating some sort of security committee to oversee the cease-fire and perhaps even some measures of demilitarization to remove the most potent weapons from the hands of all the parties, perhaps even including the PLO.

The goal is to restore the authority of the Lebanese government as an entity with responsibility and a lot more capacity to maintain order. Only by negotiating an end to the Lebanese factional fighting, say those involved, will it be possible for all the principal parties concerned to resolve the missile crisis by, as one of them puts it, "running the reel backwards."

This means, in effect, undoing the chain of military attacks and deployments by the Christian Phalangist militia, the Syrian Army, the Israeli Air Force and assorted other elements that led inexorably to the Israeli shooting down of Syrian helicopters, the Syrian introduction of SAM air-to-ground missiles, and the Israeli threat to wipe the missiles out.

Down the road would lie the prospect of a Syrian withdrawal, the neutralization of the PLO and creation of a responsible central Lebanese government. It is a long road, blocked by intense Lebanese political rivalries, ancient hostilities and the overarching Arab-Israeli conflict, at the heart of which lies the Palestine issue.

But the Arab League's emergency committee, however modest and inconspicuous its efforts at the moment, has picked the right way to start.