Listening to Secretary of State Muskie ruminate upon his first five turbulent months in office, you get, first of all, the impression of a man grown increasingly comfortable with the challenges of the job and more than willing to talk about them.

But you also get the sense of a man increasingly uncomfortable with the working conditions -- and reluctant to talk about that. He will not specify for the record exactly what he thinks needs to be done to curtail the role of the National Security Council staff or its chief, national security adviser Zbigniew Brzezinski. He will not discuss "personalities."

But the conclusion you come away with is inescapable; if there is a second Carter administration, there is almost certainly going to have to be some early resolution of the continuing struggle between the NSC staff and the State Department over who is responsibile for what in the conduct of diplomacy, and in the making -- and official stating -- of policy.

All this is another way of saying that when you are weighing the foreign policy unknowables of Ronald Reagan against the record of Jimmy Carter, you have to take into account a significant unknowable about President Carter. If he chooses to go on managing foreign policy in the same old way, my hunch (and it is not more than that) is that he will have to do so without the services of Secretary Muskie.

But if Muskie prevails, even perhaps only in a matter of degree, predictions are somewhat easier. This is the first of two reports on a long luncheon conversation in the secretary's eighth-floor dining room in which he set forth in a concerned, contemplative and confident tone his developing views about foreign policy priorities for the long haul, about how to deal with the Soviets, about the utter necessity to push hard for ratification of the Salt II treaty, about the requisites of diplomacy and the role of the secretary of state.

"What I like about diplomacy -- probably the only thing I like," he says, "is that it is conducted n such a civilized way." As for his celebrated temper ("I have it, I use it, and I can lose it"), it doesn't work in diplomacy: "You discuss your differences, you don't raise your voices, so that if a point comes when some display of emotion is in order, it's more credible."

He dislikes the "confrontational" approach: "You can't have a dialogue with the Russians if you're shouting at them all the time." He thinks he has a "healthy relationship" with Soviet Foreign Minister Andrei Gromyko and finds it "interesting" that more than once Gromyko has interrupted his translator "for having translated what he said too harshly."

It could be just a ploy, he concedes -- he does not give the impression of having illusions about the Russians. On the contrary, he finds them "not easy to read" and puts at the top of his list priorities for the next four years the job of "taking the right reading of the Soviet Union."

His own reading? Skeptical. He thinks the Soviet threat has been overdone in the campaign: their "limitations and shortcomings don't get much attention." But the Soviet Union "surely is a superpower and must be respected."

While he remains "ambiguous," for example about the Russians real objections in Afghanistan, he doesn't entirely discount their claim that their purposes are limited to dealing with "instability" in a neighboring country of vital security interest to them. And so he believes that ultimately the Soviets will see it in their interest to withdraw for the sake of restoring profitable relations with the West -- if steady pressure is kept on them to do so.

He thinks the U.S. grain embargo has, and will continue to, cost the Soviets heavily, and that the cutoff of technology is a serious loss to them. The trouble, he admits, is that the administration oversold the idea that these measures, plus the Olympic boycott, would be "punitive" enough to force the Soviets to withdraw from Afghanistan before they have restored it to reasonable stability.

It is, in short, a balanced, cautious estimate: "The Soviets are competitive -- they're not going to abandon their effort to prove that their kind of society is right." But they are also encircled, suspicious, beleaguered.So while he would resist Soviet encroachments, Muski thinks the "question really is the extent to which the Soviet Union can be made to feel comfortable on this planet -- without being expansionist."