The government's special nutrition program for low-income women, infants and children (WIC) sharply reduces later Medicaid health outlays for the mother and child and also results in improved birthweights, according to an Agriculture Department study.

The long-awaited study has special significance because of a protracted dispute over a study four years ago that came to the same basic conclusion -- that WIC enhances the health of the mother and child. Despite its findings, and for reasons never made clear, the Agriculture Department altered the summary statement of the 1986 findings to play down the beneficial health effects.

The new study, in contrast, was hailed by the current agriculture secretary, Clayton Yeutter, as showing that "Medicaid-eligible pregnant women who participate in the WIC program have healthier babies who require less Medicaid assistance after birth than those of low-income pregnant women who don't participate."

Catherine Bertini, assistant secretary for food and consumer services, called the findings "exciting." Robert Greenstein, director of the department's Food and Nutrition Service in the Carter administration and now head of the nonprofit Center on Budget and Policy Priorities, said, "This reinforces the earlier study."

Senate Agriculture Committee Chairman Patrick J. Leahy (D-Vt.) said that the new study "is solid proof that WIC works in providing essential food and nutrition to hungry mothers and children."

The study was released as Congress moved toward a final decision, possibly this week, on funding for fiscal 1991 -- expected to be set at $2.35 billion, about $200 million over fiscal 1990. The funds are estimated to allow about 52 percent of eligible low-income pregnant women and children to participate. In 1990 about 4.5 million women and children received special food supplements when found to have nutritional deficiencies that could affect the health of the mother and child.

The study, conducted by Mathematica Policy Research Inc., found that in five states, when mothers received program foods before birth, the government's Medicaid spending averaged between $277 and $598 less for health care of the mother and child in the first 60 days after birth than in cases where the mothers did not receive special prenatal foods.

Looking at program cost-effectiveness, the study found that "for every dollar spent on the prenatal WIC program, the associated savings in Medicaid costs during the first 60 days after birth ranged from $1.77 to $3.13."