FOR A NUMBER of years, the infant mortality rate in the United States has been a subject of some consternation; by this measure, which is frequently used to determine the level of civilization of a society, the United States has consistently ranked well below Western Europe and some of the other industrialized countries. Besides, the problem is concentrated among the poor and the black, and babies of young mothers who are badly nourished are in special danger.

In 1973, as part of an effort to do something about it, the Women, Infants and Children Supplemental feeding program (WIC) was enacted. The program provided dairy product, orange juice and other essential foods to low-income pregnant women who were diagnosed by physicians as having nutritional problems. This program was the brainchild of nutrition researchers and pediatricians who felt strongly that the combination of prenatal medical care and nutritional help would make a difference in the health of both mothers and babies.

For the first couple of years, the program looked like a depressing replica of so many other efforts to break into the poverty cycle. It was plagued by administrative difficulties and lethargic management, and it was not easy to persuade the mothers to take the food. Lots of tired, pregnant women found the prospect of carrying two weeks' worth of milk home on the subway more than they could manage.

But with a few changes here and there -- more enthusiastic management, a change from distributing the food itself to distributing vouchers to be cashed in at the local supermarket, and time to work out the snags -- WIC has turned into one of the genuine success stories of federal social policy.

Two carefully controlled studies, one at the Harvard School of Public Health and the other in Waterbury, Conn., found that the program has made a big difference. Infant mortality dropped among babies born to mothers who were getting food through the program, compared with a similar group who did not. Participating mothers had fewer low-birth-weight (under 5-1/2 pounds) babies. Such tiny babies often suffer complications, and frequently don't pull through. The program also picks up infants who start out dangerously small, and provides the formula and other food to help them catch up to their normal weight. The evidence is that this is working too.

This news is important. In the somewhat murky world of social program evaluation, the clarity of these findings is extraordinary. It is good that something is working and that it is working to help resolve this most basic human problem. Among all the budget reductions, funds for this program are going up, and that is good too. Some programs do work.