IN A SPEECH before a group of judges last August, Supreme Court Justice John Paul Stevens suggested that the court's workload could be reduced if Congress itself were to settle the ambiguities about the laws it passes, rather than leaving it to the courts to clarify those provisions about which there is confusion. It is obvious that the justice has never been a politician himself or he would have realized that often Congress is ambiguous on purpose. Rights and benefits are lavishly created -- these are politically attractive tasks -- while the details of how the thing will work or who will pay -- the hard parts -- are left to the poor administrative agencies and courts. That's what happened, for instance, when something called the Pregnancy Discrimination Act was passed by Congress in 1978, and that's why a controversial and potentially costly problem landed at the Supreme Court this week.

Six years ago, the Supreme Court, in the case of General Electric v. Gilbert, held that failure to provide female workers with disability benefits for pregnancy was not sex discrimination as prohibited by Title VII of the Civil Rights Act. Congress, wishing to reverse this decision and establish these rights for women, passed the Pregnancy Discrimination Act, which said that employer disability and medical plans could not treat pregnancy differently from the way they treat an illness or disability. That's all fine and clear so far as female workers are concerned, but the important and expensive question was this: where such a health plan provides family coverage, can pregnancy benefits be provided only for female employees and not for the wives of male employees? If a company makes such a distinction, is it discriminating against the male employees?

It's not as if legislators failed to see this question. Witnesses before congressional committees raised it, and the committees considered it, but opted to duck. The Senate committee report, for example, plays around with the issue, raises a few straw men and then dispatches it to the courts with the directive that "the question in regard to dependents' benefits . . . be determined on the basis of existing Title VII principles" -- whatever those are.

The reason for the evasion, of course, is money. Congress preferred to pretend that this bill would not cost the private sector much. The number of women in the work force who are pregnant each year is only a fraction of the women in the population who would be covered under their husbands' health insurance policies. The cost estimates for putting this legislation into effect ranged from the AFL-CIO's $130 million a year to industry estimates in the bllions. Those estimates at the lower end assumed that only female workers would be covered.

As Congress surely must have foreseen, legal battles over the meaning of the statute began immediately. Male workers have sued to clarify their rights under the law, and the lower federal courts have issued conflicting opinions. A small fortune undoubtedly has been spent by government agencies, employers, litigants and courts. This week, the Supreme Court agreed to take the heat and settle the question. As is so often the case, it all could have been avoided if Congress had acted straightforwardly in a matter of great importance to employers and families, and written a law that was clear. Congress faked it.