Why is it that the terms of our public discoure -- and our familiar canons of reasoning-- are suddenly suspended whenever we are faced with the questions of medical treatment for newly born children? There was nothing especially complicated or esoteric about the regulations that were recently announced by the Department of Health and Human Services: hospitals were required to post, in their maternity wards and nurseries, a notice that the "discriminatory failure to feed and care for handicapped infants in this facility is prohibited by federal law."

But the American Academy of Pediatrics challenged those regulations in a federal district court, and its position was upheld, for the moment, on a procedural ground: the administration failed to persuade the court that it was acting quickly "to protect life from imminent harm" and that it was reasonable to forgo, in this case, the usual waiting period for public comment before new rules are put into effect.

Still, when this procedural issue is finally resolved, the question of substance will remain. On that point Judge Gerhard Gesell managed to express--quite early, and quite gratuitously --his hostility to the measures of the administration.

From the remarks of the judge and the reactions of the public commentators, one would gather that the administration had addressed a problem too inscrutable to yield to ordinary language or to the judgments of the law. Ellen Goodman worried, with many doctors, that the regulations would not allow a distinction to be made between the child handicapped by Down's syndrome and the child handicapped by the absence of a brain, or by other afflictions so profound that his prospects were hopeless. For the critics, these were matters properly left to the "medical" judgment of doctors and to that delicate, private relation between a physician and his patients.

It has become a common reflex among doctors these days to regard any matter as a "medical" question if physicians are somehow involved in it. But with the benefit of more strenuous reflection it should become apparent that the new regulations raise no question that is distinctly "medical." Nothing in the regulations would foreclose the need for doctors to make assessments, from one case to another, on the condition of patients and the prospects for treatment. What the new regulations reach are those cases in which the afflictions of the child could be treated practicably by surgery; where the doctors and the parents would agree to operate; but where the decision is made, nevertheless, to hold back medical treatment because the child is retarded or "handicapped."

The judgment, at that point, does not pivot on any medical issue but on a question of "principle": Is there something in the very condition of being retarded which establishes that people deserve to perish or that they have a lesser claim to live? Does the presence of infirmities justify a policy of withholding from the "handicapped" services or benefits that should not be affected by their disability (such as their access to education)?

When stated in this way, it should be evident that the principle engaged here is the same principle that has underlain our statutes on the treatment of the handicapped. And that is in fact the provenance of the new regulations: they were drawn by the administration under the authority of the Rehabilitation Act of 1973. To my knowledge, none of the critics who find the regulations dangerously imprecise has ever raised a question about the clarity of that statute--or of the law that has been built up now for a decade in protecting the "handicapped" from all species of unwarranted harms and exclusions.

Of course, the notion of being "handicapped" cannot be free of ambiguity. But it hardly raises problems of interpretation that are any graver than those generated by other statutes, which have not excited anything near the same alarms. Can we define, after all, everyone who is part of a "minority" that suffers "racial discrimination"? Would a preference for people with "Spanish surnames" extend to the child of Mendoza, but not to the child of Mendoza's sister, who married a man named Flynn? Is a restaurant a facility involved in "interstate commerce," even when it is separated from the highway by a dirt road, and when it seeks no interstate business? Ellen Goodman, who thought the language of the new regulations fatally sweeping and categorical has not apparently suffered any discomfort over the Equal Rights Amendment, which would ban, in a categorical, sweeping way, all discriminations based on sex (even though its proponents have been quick to assure us that they do not mean to go quite that far).

Suppose for a moment that the new regulations had declared that "it is prohibited by federal law to withhold treatment from infants on the basis of their race." Is it imaginable that the American Academy of Pediatrics would now be in court arguing that rules of this kind interfere with the "medical" judgment of doctors and the privacy of their patients?

The academy is more likely to recognize that the regulations express a principle, and that the principle cannot be affected, in its validity, by the variety of personal experiences that are brought into view from one case to another: no set of novel circumstances, no "medical" facts disclosed in any case, can possibly bear on the question of whether it is right or wrong to withhold treatment on the basis of race. And what can be said here in regard to race would have to be said, with equal force, in regard to the withholding of medical treatment from the retarded or handicapped.

The doctors are no doubt aware that parents who withhold food or medical care from their children would be subject to prosecution even if they starved their children in the privacy of their homes. The physicians must understand then, as well as anyone else, that when the law ''interferes" with this disposition of the parents, it does not interfere with anything the parents have a "private right" to do. And what is not within the privacy rights of the parents surely cannot be brought within that domain when the action shifts to a hospital and the collaboration of doctors.

If the pediatricians and their friends have been made uncomfortable by the new regulations, it is not because the administration has invaded a sacred sphere of privacy or encroached on "medical" judgment. The problem for the doctors, rather, is that the administration is challenging precisely, in principle, the moral understanding on which they have been willing to redefine their missions as doctors.

The American Academy of Pediatrics has good reason now to believe that most of its members do indeed reject the principle behind the law: in one national survey of pediatricians, carried out in 1977, 85 percent of the doctors in the sample expressed their willingness to withhold surgery for children with Down's syndrome if that were the preference of the parents. More recent surveys suggest that this perspective has retained its dominance.

The pediatricians apparently think it is legitimate to withdraw medical care from the retarded, for the same reason that they have been willing to honor the decisions made by parents to end the life of the infant in the womb who is thought to have Down's syndrome. For years doctors have been allowed to conceal, behind their claim of "medical judgment," a doctrine for taking life that cannot arise from anything in their field of competence. What they feel now, in these new regulations, is the sting of reproach; and in this case, the law has directed that reproach to the proper place.