PRESIDENT REAGAN in his Central America speech nailed down the essential point that the region matters and that the way the United States deals with events in its back yard will be taken in many other places as a measure of its constancy and steadiness. He did not prove beyond a reasonable doubt that his particular combination of policies is the one best calculated to serve American interests.

The president suggested that the choice lies between his course and an opposition that "counsels passivity, resignation, defeatism . . . while the people of Central America are delivered to totalitarianism and we ourselves are left vulnerable to new dangers." But this is not fair. Most of Mr. Reagan's critics accept his judgment of the high stakes: they want no more Nicaraguas and no more Soviet advances. On these goals there is agreement. What is questioned is the way of reaching them. The main congressional critics note, as Sen. Dodd suggested, that although Congress has ended up giving Mr. Reagan negotiating space and all the aid he has sought in the last 21/2 years, things seem to be going from bad to worse. Why? they ask. And what reason is there to think that more of the same will work?

Mr. Reagan's focus is on the Nicaraguan-Cuban- Soviet role, and with good reason. Central America, with its poverty and injustice, had long been simmering; what brought it to a revolutionary boil in the last few years has been outside stimulus and support. Yet the form of the administration's engagement in the region, its attempt to counter this intervention, has built-in problems of its own. It ignites old anxieties about the American role and magnifies some of the very factors--the American presence, the felt tradition of American interventionism--that lie at the heart of the political ferment.

In El Salvador, a reaction to the intrusiveness that is the companion and the price of American assistance is building among the very groups American policy seeks to rescue. In Nicaragua, American support of insurgents allows a nasty totalitarian- minded Marxist regime to dull the otherwise telling indictment that it is a foreign tool.

In brief, just as the United States cannot walk away from Central America because the region is too important, so it cannot take charge and dictate a solution because of the immense weight of its past involvement, which Latins remember more keenly than Americans do. That leaves the administration with a requirement to conduct a continuing policy, but a limited one.

The war is crushing El Salvador: taking an immense human toll, draining the economy, lowering the level of health and services, and so on. It is not just that the government lacks the aid to best the guerrillas; if that were the case, more aid would be the answer. It is that, notwithstanding the progress made in land reform and electoral democracy and even in human rights, the government and especially the still largely self-ruled army may not be up to the tremendous job of modernizing and fighting a war at the same time.

To avert the possibility of eventual collapse, meaning a guerrilla victory, the country needs the best political solution it can get. This is the result now being sought by the friendly and frantic democratic states of the Contadora group--Mexico, Venezuela, Colombia, Panama.

Perhaps these Latins are wrong in believing that the Marxist guerrilla influence can be contained better in the negotiating context that they are trying to promote. Perhaps each is too beholden to its domestic left to judge honestly the aggressive revolutionary thrust that is some irreducible part of the guerrillas ruling Nicaragua and ravaging El Salvador. Successful precedents for the approach they commend are few and far between. But no American policy that swims against the Latin current will get very far. And as high as the stakes are for the United States, they are higher for the Latins, whose plain self-interest is to slow down the Marxist revolutionary train before it reaches them.

These considerations find expression, we think, in three policy goals:

1) Congress should vote the president the Salvador aid money he seeks. There is a war on, and the government side deserves to be supported, especially if it moves toward negotiations.

2) At the same time, the administration should be expected to walk through the negotiating door that the Contadora group is straining to open for it. Passive "support" of this initiative is inadequate. If the initiative is not actively encouraged it will be overwhelmed by the sheer weight, pervasiveness and energy of American policy.

3) Meanwhile, the administration must find a way to disengage from its support of insurgents bent on overthrowing the Sandinista regime in Nicaragua. The necessary mission of interdicting arms from Nicaragua should be confined to methods that do not refurbish the old, politically crippling image of the United States as an interventionist power.

Would such a policy of generous aid to El Salvador, diplomatic cooperation with Latin friends and non-intervention in Nicaragua work? There is uncertainty and risk aplenty in it, but less, we believe, than in the president's current policy of generous aid, its own diplomatic preferences and intervention in Nicaragua. The current course has the further disadvantage of being demonstrably unable to gain the bipartisan, executive-congressional consensus that is the only conceivable basis for a policy with a fair chance for success.