WHEN A WOMAN who is working has a baby, what should her employer be free -- or required by law -- to do? Should she have a right of return to the job? Traditionally, this has been an issue settled privately. Now, in a reflection of the changed role of women, there are moves to impose a partial public solution as well. The current leading example is The Family and Medical Leave Act of 1987, approved by a House labor subcommittee last month.

The bill does not simply deal with pregnancy. The women's groups supporting it want to provide maternal benefits, but without creating sex distinctions in the law. Their way of doing both is to broaden the coverage. The bill would require employers of more than 14 people to provide up to 26 weeks of unpaid leave to any employee with a "serious health condition." That would include but not be limited to the temporarily disabling effects of childbirth. Such employers would also be required to provide up to 18 weeks of "family leave" to any parent on the advent or serious illness of a child. A worker could also take such leave if it were needed to care for a seriously ill parent. In theory, a woman who had a child would be entitled to both some weeks of leave from category A and the full 18 weeks from B. In addition to giving her back the same or an equivalent job on her return, the employer would have to keep up during her leave any health insurance payments made before.

Opponents led by the Chamber of Commerce have attacked the bill on grounds that it would inflexibly impose on all business an enormous extra cost, and weigh down small businesses especially. The opponents say the advocacy groups and sponsors in Congress, prevented by the budget deficit and political climate from creating new public benefits in recent years, have turned to legislating private benefits instead, and hiding the costs off budget.

Proponents respond that:

1. The cost is overblown. The leave would be unpaid (though the bill would require a study of paid leave). Because they'd be without pay, not that many people could afford to take all the leave, while many firms provide some leave already, so that a lot of the cost is already being borne.

2. Large and unionized firms tend to provide more such leave than small. It's easier for them; their resources and turnover both are greater. Small firms are thus where the problem and burden both are greatest. The small-business exemption in the bill is an effort to balance these considerations. About 85 percent of businesses would be excluded, but only about 20 percent of workers.

3. The larger issue is that society has come to depend on having women work. Social preferences aside, the economy requires the labor, just as families -- and the businesses from which they buy -- require the income. The double role puts women -- and families -- under enormous strain. The society needs to confront the problem more directly than it has.

Our instinct is to agree with this. We admit to some uneasiness about the bill as now expansively drawn. It is not just another labor standard. It casts a wide net in new territory; no one really knows how much it would be used or cost. To some extent it is an effort not merely to accommodate but to validate new roles within the family, and government has always been clumsy at this. But if the bill goes too far, it goes in the right direction. Women bear an unusual and not fully acknowledged burden in the present system. Children pay part of the price. Both could use some more suppor