The House Select Committee on Children, Youth and Families-whose members range across the political spectrum_has issued a 163-page report documenting widespread need for every form of child care and arguing persuasively that government child-care subsidies for low- to moderate-income families end up costing government less than maintaining the families on welfare.

The report, in the words of committee Chairman George Miller (D-Calif.), is probably the most comprehensive look at the child-care system to come out of Congress in more than a decade. What is particularly encouraging about it, however, is that it has been fully endorsed by conservative members of the select committee, including Rep. Dan Marriott (R-Utah), the ranking minority member.

Asked at a press briefing whether this signals a turnaround in conservative opposition to a federally assisted child-care system, Marriott replied bluntly: "There is still the conservative mentality that the federal government has little role to play in anything. I agree with 90 percent of the conservative philosophy and 10 percent I don't agree with. This is one area they need to get back into the real world on. It will be very interesting to see what kind of response Budget Director Dave Stockman and company have to this report." The report does appear to signal that Congress is coming to grips with the real world. With one cautionary note -- namely, that the jury is still out on whether infants are better off with their parents or at child-care centers -- the committee recommends a wide range of initiatives designed to create a partnership between governments, the private sector, and parents to establish a comprehensive, affordable, safe and dependable child-care system.

"The report is responding to historic change in American society, the economy and the American work place," said Miller. "It simply cannot be ignored any longer by Congress."

The committee, which held six hearings on child care around the country, found a number of startling situations. In California, according to the report, there are an estimated 287,000 migrant children eligible for subsidized care, but only 2,880 are in subsidized centers. The report cited testimony that an estimated "95,000 are 'at risk' -- left alone or in the care of other young children for an average of 43 hours a week. It is estimated that 2,600 children under 3 years of age are left alone in cars, in boxes at the end of rows in the fields, or in nearby tents; and one fourth of the deaths of children under 14 are caused by drowning in irrigation ditches and canals."

The report documents a strong correlation between lack of child care and welfare dependency, ranging from teen-age mothers who can't finish their education because there is no one to care for their babies, to divorced mothers who can't work because they can't afford or can't find child care. In Utah, said Marriott, 90 percent of the people on welfare are divorced mothers with young children. The average child-care cost is $180 a month. Utah now gives $108 a month in state and federal child-care subsidies to welfare families so the parent can work. "It has reduced welfare costs and increased the number of welfare people" earning income by 122 percent, said Marriott. In January 1983, for example, only 920 families receiving welfare, or 8.1 percent of all welfare families, had any earned income. With the subsidy, the number jumped to 2,046, or 17.4 percent, by June 1984.

"You can pay $108 for child care or $400 for welfare," said Miller.

The report recommends that Congress examine the tax system to find further ways of encouraging corporations to help employes with child care, that Congress require states that get child-care subsidies to have adequate licensing, inspection and training requirements for day-care centers, that federal subsidy for child care be increased, and that funds be made available to help nonprofit organizations start before- and after-school care programs and information and referral services. It also recommends that Congress work with the private sector to develop leave and personnel policies that do not penalize employes for staying home to care for infants, and that Congress provide grants to help school districts that want to develop programs for 4-year-olds in the public schools.

The overriding message of the report is that spending money on child care makes good fiscal sense. Migrant children in boxes, migrant children drowning in irrigation ditches and mothers on welfare because they can't buy child care makes no sense at all.