FOR THOSE who had hoped the Supreme Court would speak definitively about the legal obligation of employers to pay equal wages for jobs of "comparable worth," last Monday's decision was a severe disappointment. The justices specifically avoided that issue in a case in which they had been asked to face it squarely. Instead, they disposed of the matter before them in a way that neither closes the door to comparable worth litigation or opens it.

Probably that is just as well. The concept of comparable worth, unlike its respectable relative --equal pay for equal work -- is difficult to grasp and would be complex for employers, let alone judges, to administer. It asserts that the intrinsic value or difficulty of each job should be compared with that of other jobs offered by the same employer and wages set accordingly.

Comparable worth has much going for it as a theory. There ought to be a stronger relationship than there is between the value or difficulty of any job and the wages the worker receives. But the theory is so alien to the way wages have long been set in this country -- by labor negotiations or by the labor marketplace -- that putting it into place would be exceptionally difficult. In its ultimate form, for example, it would require calculations line comparing the wages of schoolteachers with those of subway drivers. In one court case in which the question of comparable work has arisen, nurses in a public hospital sought pay equal to that of other public employees doing jobs of equal value in non-nursing fields.

The theory is especially attractive right now as the other half of equal pay for equal work. That legal requirement has forced employers to stop paying lower wages to women than they pay to men for doing the same job. Comparable worth is being used in an effort to get a better balance between the wages paid to women and to men for doing jobs of similar but not identical content.

Instead of plunging the judicial system into this morass, the five-man majority of the court stuck closely to the facts of the case it decided Monday: The female guards in an Oregon jail were being paid 25 to 30 percent less than were male guards. Because the jobs were not identical -- the male guards each had more prisoners to guard and the female guards did much clerical work -- the equal work for equal pay requirement did not apply. However, the justices ruled that the women are entitled to try to prove in court that they were illegally discriminated against because their wages were set at that level solely because they were female. The women may well be able to prove that, since the county's own evaluation study of the two jobs rated the women's work at 95 percent of the men's work.

Not many cases are likely to come along that either fit this narrow formula or demonstrate so clearly the weakness of the equal-pay-for-strictly-equal-work rule. It may be that the court's ruling is sufficiently broad to permit the judicial system to handle the worst of the unequal-pay-for-almost-equal-work cases. But if it isn't, and if employers kepp up that olds practice of paying women less simply because they are women, the pressure for congressional or judicial adoption of something like comparable worth will continue to grow.