Men and women are different. Sometimes the differences don't matter, sometimes they do.

Do gender distinctions matter when it comes to military service? The U.S. Supreme Court has agreed to tackle that throny issue, to weigh whether a male only military draft constitutes unconstitutional sex discrimination.

A generation ago, most Americans would hardly have considered it a serious question. But two things have happened in the interim. First, the military has changed, relying less on physical prowess and brute strength and more on technical skill. Second, social attitudes have changed. We are more keenly aware than ever before that the acceptance of generic distinctions in one area can be used to buttress discrimination in another. Will it really matter, in the push-button war of the future, whether the fingers on the buttons belong to men or women?

Of course not. But push-button warfare -- which is to say nuclear war -- may be the least likely of the real possibilities. What seems most likely is the sort of fighting that took place in Vietnam. Can anyone really suppose that the United States would have been better off in Vietnam if half its fighting force had been female?

To the extent that the draft would be relied upon for conventional warfare, doesn't it make sense to draft only men? Isn't that one of the cases where the differences between men and women do matter?

But not every GI served in the trenches of Vietnam. Would it have mattered if the company clerks, the supply sergeants, the computer operators, pilots, radar technicians and intelligence operatives had been female? And if not, what is the point of excluding women from the draft?

My own military service, as a post Korea draftee, was spend in a public information office, doing work that a woman could have performed at least as well as I. But my basic training was as an infantryman. Theoretically, at least, I might have been reassigned to a rifle unit, where my sex might have made a considerable difference.

Wasn't it to America's military advantage that, in the case of war, the draftees in my unit could have been assigned to front lines, or wherever they were needed?

Of course it was. But it was also true that some of the men in my unit would have been less competent -- in strength, marksmanship and courage -- than a lot of women I know.

So why wouldn't it make sense to draft without regard to sex and then assign individual soldiers on the basis of their particular qualifications?

The answer, in a word, is: efficiency. It is a fact that some women are stronger and hardier than some men, but it is also a fact that, taken at random, as in the draft, men are more likely to have the physical and temperemental qualities required of a fighter.

It is simply too inefficient -- too costly in time, money and flexibility -- to draft randomly when the need is for soldiers with qualities far more likley to be found in men.

The point of a military draft is not to establish sexual equality in the nation but to be prepared to fight, and win, a war. I expect the Supreme Court will take that fact into account and rule that a male-only draft is both sensible and constitutional.

Such a decision would make a lot of people unhappy. For even though it would still be possible for women to serve in the military -- as volunteers and as adjuncts to fighting men -- a male only draft would officially sanction the notion that men and women are different. It would sanction discrimination, whether against women (by presuming their unfitness for combat) or against men (by exposing them unequally to the risk of combat).

But maybe it's time for the Supreme Court -- and for Americans generally -- to recognize that sometimes discrimination makes sense.