OF THE REAGAN ADMINISTRATION'S many intolerances, few are so pronounced as its distaste for ambiguity. In foreign affairs, it has tried to resurrect an American century that never was, promising to match the Soviet Union missile for missile and warhead for warhead, while renewing the Cold War in the mountains of Central America and the deserts of southwest Asia.

To this canvas of dollar-sign diplomacy last week came a new, but hardly unexpected, brush stroke: a drastic increase in assistance to the controlling military regime of El Salvador. Drawn, appropriately enough, from the Pentagon's increased revenue, $55 million will go to the Central American country, $25 million ostensibly to replace helicopters destroyed in a raid last week by leftist guerrillas on a military airbase, the rest to fund renewed opposition to that guerrilla insurrection against the nation's coalition of civilian and military rulers. According to Secretary of State Alexander M. Haig Jr., the United States is now committed to insuring that El Salvador will not become communist.

The Administration surely cannot forget the anger it provoked when it tried to blow the Salvadoran conflict way out of proportion, attempting to stir up a paranoic fear that Russians and their Cuban emissaries were making trouble in our back-yard. The more than $100 million in aid and 49 military advisers it dispatched then aroused indignation from foreign leaders and countless Americans, all reproaching the team of Reagan, Hang and Kirkpatrick for ignoring the all-too-apparent brutality of the Salvadoran armed militia.

And surely that team must be aware of the countless charges of witnesses to incidents of "rape, torture, and murder" by armed men in military uniform, actions the Duarte government defends as part of its progressive "land reform" policy. Recent press accounts have suggested new episodes--of 926 civilians massacred in one province less than two months ago, and of 19 lined up and shot in a San Salvadoran suburb early morning. Administration officials can dispute these accounts as propaganda supporting the rebels who have little to gain from under counting civilians killed. And they can voice their doubts about the Salvadoran left, especially since the dream of freedom in Sandinistan Nicaraugua seems less than realized. Yet we all must wonder, and ask, if the perspective our government wishes to eschew--that of a popular movement fighting for national liberation from their oppressive masters--is not, in fact, closest to the truth.

In approving further aid to the ruling government, the Reagan administration has proposed an easy answer to a problem that begs quite a bit more. It aims to buttress what it claims to be a centrist government against the competing forces of the insurgent left and the military right. As easy, perhaps, as to invoke the response of the implacable American liberal and to call American aid to El Salvador emblematic of "another Vietnam" a military embroilment in a national conflict the United States has no purpose pushing. Trite perhaps, for the troubles of the Salvadoran people might bear little or no similarity to those that plagued millions in Vietnam. But until we can hear their voices, telling us who is right and who is wrong in El Salvador, no other response seems quite as sane.