IN DISCUSSING foreign policy in this space yesterday, we set aside one fundamental aspect for today. Foreign policy entails more than "policy," more than cleverness, more than manipulation. It entails the use of national power, of which military power is a critical component. The United States cannot pretend to conduct a foreign policy that is anything but minimal, reactive and perilous unless it provides itself with a solid underpinning of defense.

But what kind of defense? You might hope that, from the evidently vigorous defense debate in which the country is now engaging, some good answers would emerge. But that is not happening. The argument over military security seems to have centered on an exchange of slogans, numbers and vibrations. Jimmy Carter says "essential equivalence" and Ronald Reagan says "margin of safety." Mr. Carter says spend 3 percent more and Mr. Reagan says spend 5. The emanations from Mr. Carter hint: don't think I'm a pushover; from Mr. Reagan: you'd better believe I mean business. The result of all this is that the argument over military security has taken on a kind of independent polemical life increasingly detached from the one thing it should be about -- what kind of defense establishment is needed , and can be provided , to ensure our security at home and to fulfill our foreign policy commitments and goals. Only when one gets a reasonably coherent sense of foreign policy ends, and economic constraints, can one begin to talk rationally of defense means.

It is just for this reason, the detachment of the debate from the tough questions, that most of the sumissions of both leading candidates have been unsatisfactory. Mr. Reagan's talk abounds in grave warnings of calamity and anti-communist alarms so boundless in scope and intensity that one might think the only logical reaction is to scurry under the bed. But then he turns and approaches the solution, in the key matter of military manpower, as though he were arranging a croquet match after tea: War, anyone? Sign up over here. His basic military prescription is: more. More of everything, as though every contingency should be equally prepared for -- a dream view confounding the candidate's supposed conservative hardheadedness. As for the ever larger sums he would write into his military budgets, it is not simply that he betrays no clear sense of what to spend the money on. He does not concede that there are real political constraints on defense appropriations of the open-ended sort he prefers.

President Carter has his own confidence problem in respect to defense. Having swung away from his earlier pledge to cut the Pentagon budget back from the dangerous heights to which he kept claiming his predecessors had brought it, he now declares that he single-handedly saved a dwindling defense establishment from GOP rack and ruin, interrupting himself only to insist that his position has not changed. Well, it did change, and we're just as pleased it did. Mr. Carter was more right the second time than the first, although neither he nor Mr. Reagan has addressed the truly disconcerting fact that what we already hve doesn't seem to work very well: machines break down, units aren't ready -- the whole sad litany.

But the change has left its own residue of popular misgivings. From Jimmy Carter, people want proof that he takes seriously the prospective threats that he is asking the country to get ready for. They want proof that the alterations he has made in his defense views, and in his view of Soviet power, proceed not from political considerations but from an honest and probing analysis.They want proof of a personal understanding that the acquistion of and the readiness to use military power, far from being politically and perhaps even morally dubious, can have a central value in keeping the peace -- and in supporting legitimate foreign policy interests.

Just what is the national security question to which the Carter or Reagan defense establishment is the answer -- or, as Mr. Carter seems a good bit readier to put it than Mr. Reagan, the partial answer?That question increasingly centers, we suggested yesterday, on the Persian Gulf: to ensure access to (even while reducing dependence on) Gulf oil, to prepare with assorted friends for the different military and political challenges that a prudent person must anticipate in the region, and meanwhile to maintain a credible strategic umbrella. To set up the problem this way is to indicate the different things that have to be done at the same time: an evergy policy stressing conservation and development of alternative sources, a diplomacy making careful use of the interests that others have in Gulf stability, an improvement in the capacity to project conventional military power into the region and close attention to a strategic force that offers effective deterrence and crisis stability.

Ultimately, the defense problem comes down to choosing which of many possible threats to credit ad deciding how large the military component should be in dealing with them. Mr. Reagan has often seemed to go for the long list of threats and to favor a heavily military approach to them. In the past at least, Mr. Carter has trimmed the list and stressed other than military ways of coping, arms control and the mediation of disputes, for instance. The dilemma for voters is that neither man's argument so far -- Mr. Reagan's oversimplified and underfunded military solutions and Mr. Carter's suddenly acquired tough-guy stance -- have been made plausibly or seriously or with a willingness to accept their logical implications.