Che Guevara, the slain Cuban revolutionary, once expressed a wish that ended up emblazoned on thousands of 1960s handbills and posters: "Two, three . . . many Vietnams . . ."

I found myself thinking the other day that he had been prescient, though not in the literal sense he probably intended. For the conflicts and pressure points overseas that are now straining and confounding American policy do not strike me at all as replicas of Vietnam. But many of our politicians, more traumatized than instructed by that miserable war, do tend to see Vietnams everywhere. The quagmire, in other words, is largely intellectual this time around, not political and military. And it is my sense that until people on Capitol Hill and in the administration have pulled themselves out of it, we will not be able to have a sound or workable - or liberal or humane - foreign policy.

I'm not about to call for a D-Day invasion of Angola or even a big Dirty Trick in Kabul. The point is not that we should start intervening everywhere, but rather that we need to acquire the ability to think about things abroad as they are - as distinct from always seeing in them cautionary, if farfetched, parallels to what happened in Southeast Asia. "Vietnam, it's the theme music for everything that's happening around here," Sen. Charles Mathias of Maryland observed not long ago. He added, "But people are beginning to make a conscious effort not to be overwhelmed by it." The remark seemed to me especially important coming from Mathias, an anti-war Republican who could by no stretch of the imagination be accused of redbaiting or jingoism. Increasingly, in the past few months, he has been indicating his discomfort with what he has taken to be a passive-to-paralyzed stance on the part of the government in its dealings overseas.

What are the features of the Vietnam mind-set? Well, first there is the "worst case" scenario-making, a habit normally (and justly) associated with the right-wing military, but these days being indulged by the liberal left. For just as the Pentagon brass have a way of perceiving potential attack and obliteration in nearly everything the Russians do, so in other quarters now the most modest American contribution to another country's defense is regarded as, inevitably, the trigger to a 500,000-man involvement in a doomed and morally suspect war. It's as if it will all be automatic and unpreventable - even though that's not the way the American engagement in Vietnam came about and is even less likely to be the pattern in that war's aftermath.

There is also the Groucho Marxclub syndrome. I am thinking of the late comedian's comment that any club that would have him was one he wouldn't want to be a member of. It has become a staple of post-Vietnam thinking for many that any foreign (especially Third World) leader who is friendly to us is probably not worth having as a friend, whereas anyone on the other side may be assumed to enjoy the allegiance of the people. The "right" side may be defined simply as whichever one we're not on.

It is all very moralistic, but you will have noticed that it avoids like the devil any articulation of our own foreign-policy interests or values or aims. And that absence, both in the deliberations of Congress and the diplomatic enterprises of the Carter administration, is what has compelled people like Mathias to start pushing for some verbal formulation of what we are about. God knows, this is something to be restrained about, when you consider the corrupt use to which our mottoes have been put in the past, and our painfully won new sophistication about the limited relevance of our Fourth of July rhetoric to many societies around the world.

But policy and purpose don't need to be bombast, or florid sampler writing. Mathias, for example, known in the awful lingo of the past couple of decades as a foreign-policy "dove," can nonetheless enuciate a plausible and straightforward reason for American concern with the fate of black Africa that is neither cynical nor sentimental. He speaks of the Soviet-financed and inspired Cuban presence there and the pressures elsewhere to the North and East as endangering an area - the Middle East - which is of clear and indisputable strategic and political importance to the United States. Does one need to be shy about saying that, or even insisting on the worth of democratic values for those who choose to try them?

I have been impressed in the past several weeks, as foreign-policy choices and considerations have been borne in on the administration, by how reluctant everyone is to stake out a position of substance or to articulate a genuine purpose. We aruge instead over means and procedures and whether Congress is usurping executive-branch rights or the administration is trying to pull a fast one - and so on, ad infinitum. It's as if we were all, the administration included, seeking any distraction and diversion from the necessity of explaining - to ourselves and the world - what our legitimate interests and concerns are.

To the extent that this skittishness is part of the Vietnam reaction, it is, I think, condescending to those countries in Africa and elsewhere that we view as Vietnam ("When you've seen one . . ."); and it also, an diplomacy, narcissistic and self-indulgent. Well, the thinking goes, we won't make that mistake again . . . no sir, if anything we'll err on the other side . . . we've suffered too much for our guilt and bad conscience . . . the goal of American policy is to remain pure . . . if you don't do anything, you can't do something that is less than perfect, and we have a lot to atone for.

It is, of course, an illusion that a great power can conduct its affairs on such a basis, and it is no less an illusion than those earlier ones to which we marched into the swamps of Indochina. The terrible danger is that we might drift along on this lazy tide until the president (and the Congress) is pressed to some desperate, convulsive reaction at a point and in a place much riskier than anything that is going on now.

What I am saying is that I think Jimmy Carter needs sorely to articulate to this country and to the rest of the world what his administration takes our vital interests and priorities in foreign affairs to be, and to formulate consistent, unambiguous steps to protect and advance them. He needs to make the Soviet and Cuban adventures cost something. He needs to show he is serious and persistent in those things.

I suspect that he will get support from unexpected places on Capitol Hill if he does, since more and more people there seem to be getting bored with their own post-Vietnam bemusement. It is also my impression that, under great provocation from abroad, Carter himself is beginning to move. If he does so in time to avoid the likelihood of convulsive action later, it will have been, in a sense, an improbable and unintended gift from Che Guevara's heirs.