GIVEN THE NATURE of Middle East politics, only the foolhardy will rush to read a benediction for the Reagan peace initiative. But if, as it now appears, the president's plan is dead, it may be time to acknowledge that American diplomacy cannot play a central role in resolving the Palestinian problem. A period of passivity for American diplomacy may be in order.

Administration officials, of course, have been at pains to deny that the president's plan has been dealt a mortal blow by King Hussein's decision not to participate in negotiations over the future of the West Bank and Gaza. But without Jordan's participation there is, for all practical purposes, no Reagan plan. It is Jordan which must -- along with Israel -- implement the settlement Reagan envisioned.

Some suggest that Hussein's action is merely a tactical ploy, intended to shock other interested parties into taking new and more supportive positions. But this is probably wishful thinking. In any case, Hussein's decision will be reversed only if he gets new support from those he feels let him down this time, and that is not a promising prospect.

So who killed the Reagan plan, assuming it really is moribund? And what lessons can be drawn from this latest episode?

In a formal sense, Hussein obviously is the one who bears responsibility for the fate of the American proposal. But it will just as obviously be argued that Hussein scarcely enjoyed unlimited freedom of action. Even if he might have behaved more courageously, he could not have been reasonably expected to respond positively to the plan without getting more support than he did from the Reagan administration, the moderate Arab states or the PLO.

Many critics blame the plan's downfall on the terms of the initiative itself. The proposal, this criticism runs, required Hussein to take large risks. In ruling out a Palestinian state and in denying a direct negotiating role to the PLO, it virtually insured the PLO's opposition. To have participated in negotiations with Israel, then, Hussein would have had to defy the PLO and to usurp the PLO's role as representative of the Palestinians, conferred in 1974 by the Arab League.

The Reagan plan made sense, this criticism continues, only if it is assumed that, in the face of PLO and other Arab opposition, Hussein was prepared to proceed on his own, if necessary, and make a separate peace with Israel. But Jordan is not Egypt, and Hussein cannot be expected to run risks Sadat could run, the critics argued.

At the very least, he needed the kind of American support that the Reagan administration would not, or could not, give. In the period after the peace plan was unveiled, it is argued, the United States did not establish its credibility by demonstrating a willingness and ability to moderate Israeli behavior, whether in Lebanon or the West Bank.

The Reagan initiative should have been more forthcoming, the critics argue, on the issues of recognizing the PLO and the right of self-determination for the Palestinians on the West Bank and Gaza. These terms, together with a greater display of firmness toward Israel, presumably would have elicited a positive reply from the PLO, hence from Jordan.

This is the familiar argument that the key to a last Mideast peace must be found in America's determination to pressure Israel into accepting "reasonable" terms for settling the Palestinian issue. But to accept this view, the Reagan administration would have to invert the logic of its initiative. That logic was not one of exerting pressure on Israel but of generating pressure within Israel and within the American Jewish community, in the hope of forging a new consensus in support of the president's proposal.

The indispensable condition of such a strategy is that it enjoy Arab cooperation and support -- at the very least Jordanian cooperation and support -- else internal pressures for change in Israel and in the American Jewish community cannot be expected to materialize. Were the administration instead to focus increasingly on Israel, now that the hoped-for Arab response has not been forthcoming, it would betray the ostensible meaning of the plan, which does not look for Israel to initiate but to respond.

Such a departure would also succeed in uniting elements in Israel and in the American Jewish community that are now at odds with one another. The opposition of the Begin government to the Reagan initiative would then appear only reasonable to those who until now have not found it so, for an amended Reagan plan would take on a meaning that most of the Begin government's opponents would also find threatening.

For better or worse, the administration is probably stuck with its original plan. In the immediate period ahead, it might be tempted to undertake modest departures from the course it has marked out, but these are not likely to alter the shape of things.

There is a lesson to be learned from this latest venture in Middle East diplomacy, though it is hardly the lesson that is commonly drawn today.

At bottom, the Reagan initiative is but another version of the ideal that so captured the imagination of the Carter administration: a comprehensive Middle East peace. And the fate of the Reagan plan is but another proof of the futility of making a comprehensive peace the objective -- indeed, the principal objective -- of America's Middle East policy.

Although the Reagan plan ostensibly required only a Jordanian response, events have shown that Jordan's response is -- and will remain -- conditioned by the PLO's response, which in turn depends on theinterplay of forces in the Arab world. This was the case even when the PLO enjoyed a certain independence, by virtue of its possession of a territorial base. It is all the more true today, when the PLO is dispersed among Arab states. The PLO increasingly represents little more than an odd mixture of factions that are the playthings of their respective patrons.

The Arab states remain incapable of acting collectively on the Palestinian issue save in terms that effectively shut the door on any negotiations.

One, Syria, bitterly opposes a settlement, since almost any conceivable settlement is considered to detract from Syrian interests. Another, Saudi Arabia, is reluctant to pursue any clear course, torn as it is by its many fears. Still another, Egypt, is receptive to the American plan, but it is no longer disposed to champion a cause that has earned it little but Arab enmity.

In the wake of the Jordanian decision, it is feckless to believe that a revised American initiative might do what the original proved unable to do. If Hussein is unwilling, or unable, to undertake negotiations on his own with Israel and to conclude a separate peace with the Jewish state, there will be no prospect for diplomacy to play a role in shaping the outcome of the Palestinian issue.

The Reagan initiative will then pass into history, and the Palestinian issue will be decided by the debate now going on within Israel. y Robert Tucker; Robert Tucker is a professor of international relations at Johns Hopkins University.