WOMEN in the US armed forces performed admirably during the Gulf war. More than 35,000 American women participated in Desert Storm. They served in nominally "noncombat" roles; but in modern warfare the distinctions often blur. Besides serving in support and maintenance units, women piloted supply helicopters around the battlefield and served in missile crews. Eleven women died, and two were captured.Pointing to examples of skill and bravery by females in near-combat conditions, many women in the military and in Congress - notably Rep. Patricia Schroeder (D) of Colorado - think the time has come to let qualified women fight. Last week the Senate followed the House's earlier example and passed a bill authorizing - but not ordering - the armed forces to let women crew combat aircraft. Congress's signal in this timely legislation should be heeded by the brass. Many supporters of the legislation hope that eventually women will serve in other combat units, as on fighting ships like aircraft carriers and destroyers, and even on the front lines in infantry, tank, and artillery units. Proponents see the issue as one of basic fairness: Since combat - or, in peacetime, combat training - is a major credential for promotion in the military, women should have the same opportunities for advancement as men. Fairness for women is, indeed, important. But in the case of women and combat, the ultimate issue is the readiness and effectiveness of America's fighting forces. The bottom line isn't equity, but national security. Few would deny that women are competent to serve in many combat roles. Infantry and artillery duties demand physical strength beyond that of many (though not all) women. But in today's high-tech warfare, much of the fighting is done with sophisticated weaponry whose operation calls on mind more than muscle. There is no reason to doubt that women possess the dexterity, judgment, and nerves needed for such weapons. Yet fighting effectiveness is a matter of group dynamics as much as one of individual capabilities. Teamwork and esprit de corps win battles more than sharpshooting or personal valor. The combat unit is not, like men's clubs, just one more bastion of male privilege. Could the presence of women in combat units larger than a warplane or battery crew alter the group dynamics in unpredictable ways? Would the usual fissures between the sexes, which can be sealed in most contexts, widen in the uniquely stressful environment of combat - thereby impairing unit cohesiveness? What about questions of privacy, hygiene, and, yes, sex? These kinds of issues must be examined carefully before women a re given a substantially wider role in combat units. Yet it must be recognized that for years the group-dynamics argument was improperly used to exclude blacks from combat units. Studies and combat simulations involving women must be performed in good faith.