IN considering their vote on an override of President Bush's veto of the family-leave bill, members of Congress should consider the results of the first large-scale national study of the effects of day care -- evidence that full-time day care, as against having a parent home, may harm children under the age of 1.
The study, supported by the Labor Department and the National Institute of Child Health and Human Development, began in 1979 with a nationwide sample of young adults, who have been reinterviewed annually.
In 1986 their children were given psychological tests and the parents were asked about the children's behavior. The parents were also asked about work and child care arrangements since the children were born.
Two research teams independently analyzed the information obtained in 1986 for about 500 3- and 4-year-olds and released their findings. Both found that scores on a word-knowledge test that predicts school performance were lower for children whose mothers had worked outside the home while the children were less than 1 year old.
The research teams differ somewhat on which children are at greatest risk.
The analysis by Sonalde Desai of the Population Council and P. Lindsay Chase-Lansdale and Robert T. Michael of the University of Chicago concluded that harmful effects on word knowledge were limited largely to boys.
But Nazli Baydar of the Battelle Institute of Seattle and Jeanne Brooks-Gunn of Columbia University reported negative effects for girls as well; they also concluded that the effects were greatly reduced if the mother worked less than 10 hours per week.
The studies did contain some good news. The researchers found that word knowledge and behavior problems were not affected if mothers worked after their children were 1 year old. If this is true, then public and corporate policies that subsidize day care for children age 1 and over would not be harmful to their development.
Still, the findings on infants are worrisome. The problem is particularly acute in the United States, where about one-fourth of mothers of infants hold full time jobs.
In Britain only about one-tenth of mothers of infants are employed full-time. Even in supposedly avant-garde Sweden a smaller percentage of mothers of infants work full time: Most take paid leaves and many work shorter hours for several years.
The administration, which maintains that family leave would mean government interference in the workplace, argues that mandatory leave would be expensive for employers.
But a survey in four states that already have similar family leave laws, conducted by the Families and Work Institute in New York City, found that only 12 percent of the businesses reported significant cost increases.
The alternative, employer or government subsidies for high-quality day care for infants, would be very expensive because more care givers are needed for infants than for older preschoolers.
The best option is for employers to provide new parents with work leaves, and the current bill is a good first step. If the Republican commitment to family values isn't just rhetoric, members of that party should join in the override.
Andrew Cherlin, professor of sociology at Johns Hopkins University, is editor of "The Changing American Family and Public Policy."