AS PART OF the Carter Administration's effort to devise a policy for welfare reform, a group of government officials have been meeting every Friday morning in a conference room at the Department of Health, Education and Welfare. At a recent meeting the discussion centered on how the government might encourage or require work of more than one million welfare mothers, particularly those whose children are in school.

"Who," interjected a legal service lawyer, "is going to take care of these mothers' children when they are out of school on vacation?"

That no one in the room had any ready answer to the attorney's question about child care would have come as no surprise to Gilbert Y. Steiner, a Brookings Institution political scientist. In his book The Children's Cause Steiner contends that the interests of children are often poorly represented in the Washington political arena.

Steiner, with the assistance of Pauline H. Milius, has written a tough-minded analysis of how political power is exercised on children's issues. He gives low marks to most of the lobbying efforts that have been made in behalf of government action to benefit children. In Steiner's view the children's cause has suffered in the government arena not because of a lack of caring about children but because of a vareity of other reasons: a broadscale, well-defined children's policy has not been clearly formulated; too few tested ideas have been advanced on how government can and should help children; various children's advocates have failed to make common cause; and responsibilities for children's programs are spread haphazardly throughout the Congress and federal bureaucracy.

Steiner is not impressed with the usefulness of the decennial White House conferences on children or the periodic creation of federal commissions. He writes that the Joint Commission on Mental Health "produced a compendium urging everything and emphasizing nothing," and that the White House conferences are more "catch basin than cauldron" from which children's policies can be effectively forged. Furthermore, he contends that the Advisory Committee on Child Development failed because its members never could agree whether policy should center on day care, guaranteed annual income, education or civil rights.

Children's health programs sometimes fail in the federal government, Steiner writes, because they are too often the result of "political accidents and back-door approaches rather than rational responses to rational proposals." It is no wonder that a law calling for periodic medical screening of poor children took years to implement and still doesn't work properly considering that the law represented "an innovation of unknown complexity and cost, without a congressional sponsor, buried in a massive bill not principally concerned either with children or with health, and scheduled by one administration to be implemented by its unknown successor."

Steiner is not surprised that President Nixon voted in 1971 a multibillion-dollar federal day-care bill, and that the proposal has not been revived in Congress. In his view government-supported day care on a large scale will become law only when there is a much broader public consensus that government should play an increased role in the education and care of young children.

The bill got as far as it did in 1971, Steiner contends, only because of a temporary coalition between labor and public interest groups variously interested in child care, early childhood education, civil rights, community change, welfare reform and women's liberation.He further shows that the bill's sponsors did not face up to the fact that their proposal would have cost billions of dollars which neither the country nor the Congress were ready to authorize.

Nevertheless, the day-care issue will soon be before the country again as the Carter Administration proposes a welfare reform plan that will urge or demand work from some welfare mothers, whose children would receive federally subsidized day care. Such a proposal would pose again very difficult questions: Should a mother's role be at home with her children? Is the high cost of day care worth the gain in making mothers work at generally low paying jobs? Should day care be merely custodial or should it be developmental? Is it fair to provide day care to the children of welfare mothers and deny it to families with only slightly more income?

Steiner finds that advocates of the children's cause would be more effective if they sharpened their issues, and followed the lead of Marian Wright Edelman and the Children's Defense Fund. Edelman's group has concentrated on such issues as the plight of children who are not in school and of children held in adult jail and prisons.

Steiner suggests that children's advocates center their attention on the Office of Child Development in HEW. This office was created to coordinate policy on children's issues but the directorship has been left unfilled for years at a time, and the agency has yet to play its anticipated coordinator role.

Another means of increasing effectiveness in behalf of children is for advocates to make common cause with groups that have a vested special interest in child services. As an example, Steiner cites the expansion of the national school lunch program which now provides free or reduced price meals to 10 million poor children. He says this good result was achieved because child advocates joined forces with the association of food service workers who gained jobs in the expanded food program. Similarly, he suggests that advocates of expanded day care should ally themselves with the American Federation of Teachers which is advocating development day care in the schools. In the past, some of the strongest day-care advocates have insisted that the schools would not perform well as day-care centers.

"The children's policy most feasible - and most desirable," concludes Steiner, "is one targeted on poor children, handicapped children, and children without permanent homes: unlucky children whose parents cannot provide them a start equal to that provided most children."

Commissions can make themselves useful by studying in detail the needs of these unfortunate children, writes Steiner. Lobbyists should urge programs targeted to disadvantaged children, and social altruists can perform their most needed service by monitoring programs to make certain they really are effectively serving the children's cause.

For those interested in helping the children's cause, Steiner has written a good handbook for more effective action.