It used to be, save in the rarest of cases, that the problem of what to do about severely deformed infants answered itself. They died, despite our best efforts to save them.

No more. Medical science can keep them from dying. But neither medicine, philosophy nor common sense is of much help in answering the excruciating question of whether, in extreme cases, we ought to.

We've had recently the case of "Infant Doe," the Indiana baby who died six days after birth when his parents decided, with court approval, not to feed him. Before that there was the celebrated case of the California parents who chose to deny to their severely handicapped adolescent son (Down's syndrome and a congenital heart ailment that denied his body oxygen) life-prolonging surgery.

The current Reader's Digest recounts the heartrending case of a Tennessee child, born in 1975 with "nothing more than a shapeless mass of wet mucous membranes" where her face should have been, "only a ragged opening for breathing and feeding . . . (and) no indication of where her eyes should be."

What is the right thing to do in these sad cases? Is so-called "passive" treatment--the withholding of necessary medical care, or of food--any more humane than a life-ending injection? (Would it be "passive" if you refused to remove such a child to safety from a busy thoroughfare?)

Should doctors (perhaps in consultation with parents) make distinctions between grotesque-looking but otherwise healthy children and those whose chances of survival are only slim, even with heroic care? Is there some line beyond which we can project a "quality of life" not worth sustaining? Is mental handicap a more ethical basis for withholding care than gross physical handicap? Is it fair to saddle parents with children they earnestly believe would be better off dead?

Clearly there is no ethical consensus. There have been cries of outrage over the decision to let "Baby Doe" (Down's syndrome and an incomplete esophagus) starve to death. The California child was adopted by another couple who found him "ripe for affection and love." Doctors managed to construct a reasonable facsimile of a face for the irretrievably blind Tennessee youngster whose 18-year-old mother found her too much to care for. She, too, has since been adopted, and is thriving.

We can agree that, to the extent that the incredible financial cost of caring for such children is a factor, the government might be of some help. But the government is of little assistance in answering the more fundamental question of whether such children should live or die.

Not that the government won't try. Two recent efforts are far from reassuring. One, a species of snitch rule, would require any hospital receiving federal funds to post the telephone number of a "Handicapped Infant Hotline." Under this rule, promulgated by the Department of Health and Human Services, anyone with information that a handicapped infant is being denied food or medical care is encouraged to place a toll-free call that would trigger an investigation.

The other attempt at dealing with the problem is the recommendation of a presidential commission that hospitals establish clear decision-making policies with regard to such cases, complete with in-house review procedures and an "ethics committee" to determine whether the handicaps are "so severe that continued existence would not be a net benefit to the infant."

What would such an ethics committee have said about the armless, legless infant who grew up and, a few years ago, successfully fought an attempt by the state welfare agency to take away her own child on the ground that she couldn't care for it? How many thousands of grossly handicapped adults would have, as infants, been condemned to death on the ground that their "continued existence would not be a net benefit" to them?

It is tempting to hope that scientific advance will render the questions easier. Recent medical history suggests the opposite. Technology will make it easier to keep more and more profoundly deformed babies alive. But the ethical question will get tougher: should we?