Almost alone among the congressional critics of the Vietnam War in the late '60s and early 70s, Edmund Muskie offered no illusions that the United States could somehow disengage without risking the loss of everything it had been fighting for.

He didn't say it didn't matter; he said it wasn't working. When he ran for president in 1972, he was equally upfront with his confession of past errors in judgment, offering no fool-proof, risk-free solutions, freely conceding the possible adverse consequences of his counsel. This combination of candor and common sense has marked his all-too-brief stint as secretary of state.

And that is why, all other considerations aside, it seems to me that the impending departure of Ed Muskie from high office on Jan. 20 was one of the larger losses in last November's vote.

The point here is not necessarily Muskie vs. Alexander Haig, although clearly that change is going to constitute a considerable part of the difference between the foreign policy approaches of the new administration and the old.

From what we have so far seen of Haig, he is obviously a fierce believer in the role of force (or the threat of it) in combination with diplomacy. Muskie, by his own admission, came out of the Vietnam experience with deep reservations about the way American force can be usefully brought to bear in pursuit of this country's interests around the globe.

For all I know, in any given situation, Muskie and Haig might wind up roughly in the same place in the end. What is clear, however, is that they would approach almost any foreign problem in dramatically different ways at the start. And nothing better illustrates the point than the emerging debate over what to do about the hostages in Iran.

The Haig/Reagan approach can only be guessed at. But assuming that no miracle brings the hostages home between now and Inauguration Day, the presumption is that the new administration will quite rightly, feel free to reconsider every "option." You've heard them all: breaking off negotiations; fixing deadlines; declaring war and making the hostages instant POWs; military action of some sort.

In short, tough talk, without much mention of the consequences.

Muskie, by contrast, is not much of a believer in tough talk without consideration of the consequences. His appearance a few nights ago on the "MacNeil/Lehrer Report" was not only vintage Muskie but perhaps as cogent an explanation as has yet been offered of the thinking behind the Carter administration's approach.

Was he hopeful, he was asked, of a breakthrough on the hostage issue before Jan. 20? "Well, I long ago dismissed hope as a useful emotion," he replied. "But one never knows, given the power struggle going on in Iran today . . . when somebody is in a position to make a decision favorable to our proposals."

What did he think of the idea now circulating of a declaration of war? Again the low-key, understated reply: "When you do that, you risk moving away from one of our two objectives -- the hostages' safety and speedy return" (the other being a solution consistent with national honor). That is, you risk getting the hostages killed.

But there are "risks" in our present strategy, Muskie acknowledged, so the new administration probably ought to go back to ground zero and "look at a lot of options." But, he went on, "when you do that, you look at a lot of options that you won't necessarily consider seriously."

In other words, the new administration may not like the look of the "options," from inside the government, any more than the Carter administration did.

Was negotiating over the difference between $24 billion and $6 billion "consistent with" national honor? Muskie refused to talk about specific sums. But his real point lay elsewhere. Rejecting the word "negotiation" in the accepted sense of bargaining, he defined the current exchanges through Algerian intermediaries as no more than an effort to arrange for "a return to the status quo ante."

That, he insisted, is the "principle" on which the Carter approach has rested all along -- "that if they will undo what they did when they seized the hostages we would do everything we can within the limits of the president's authority to undo what we did in retaliation for what they did."

Now that may still strike some people as dishonorable. But it is not exactly the same thing as paying "ransom." In any case, if you are not prepared to put the lives of the hostages in jeopardy, it makes a certain amount of sense. In his eight months in office, Ed Muskie brought an uncommon amount of good sense (among other valuable qualities) to the conduct of American foreign policy.