ANYWAY you look at it, the decision by a three-judge court last Friday to strike down the existing draft registration law is startling. Lower-court judges rarely act so boldly; they usually prefer to leave such important departures from tradition to the Supreme Court. Their willingness to abandon this protocol, however, demonstrates the speed with which the law -- as well as the country's mores -- concerning distinctions based on gender is changing.

The situation is somewhat like the one that existed 25 years ago when the Supreme Court Agreed to hear the school desegregation cases. The old "separate but equal" racial doctrine was then on its way out, underminded by changing public attitudes and by new perceptions of judges that it could not be squared with a Constitution that guarantees all persons "equal protection of the law." Now, changing attitudes and judicial perceptions have raised a question about every law that discriminates on the basis of gender.

Last year the Supreme Court said that, to be constitutional, any classification on the basis of sex "must bear a close and substantial relationship to important government objectives." The three lower-court judges applied this test to the draft registration law. They said the government's main purpose in excluding women form registration was "to maximize the flexibility of [military] personnel management." But the evidence presented to them, they said, did not support the conclusion that all-male draftees would be more easily managed than an integrated group. The steadily increasing number of women in the military, studies of the way they are used and testimony of military leaders all point in the other direction, they said. Most of the documentation ofor this view came from hearings at which military leaders backed the administration's proposal to register both men and women.

The judges carefully pointed out that they were not dealing with the draft itself nor with the women-in-combat issue. They noted that drafts to do not have to be random in nature -- there was once a doctors' draft -- and that under present military assignment policies women are used to free men for combat.

Regardless of how this case is finally decided, its impact on other litigation and government policies is likely to be big. It will help to focus the attention of other judges on sex discrimination cases, and it may discourage legislatures from passing laws that treat men and women differently.

It is important to note that the argument over this aspect of the registration law has nothing to do with the bulk of current protests and refusal to register. Both the question of the merit of a draft and the question of the wisdom of a registration program at this time are separate but equal issues. If the court rules that male-only registration is unconstitutional, either the lists now being compiled will be destroyed or the names of women will be added to them. If it upholds male-only registration, nothing will change. Either way, this part of the protest against registration is in the hands of the judges and provides no justification for young men to refuse to sign up.