Labor unions, religious groups and children's advocates have launched a joint lobbying effort for a $2.5 billion national child care bill that would establish federal child care standards, help low-income families pay for care and expand day care services across the country.

The bill, to be introduced in the House and Senate this week, represents the first serious congressional effort in 16 years to create comprehensive federal child care programs and policies.

The proposed legislation would use 75 percent of its funding to subsidize day care for families whose incomes are not more than 15 percent above a state's median income, sponsors said.

Other funds would be used to help states give grants and low-interest loans to start more child care services, to train people to provide child care in their homes for groups of five or six children, to pay for extended hours at preschools, to develop resource and referral services, and to enforce standards.

Proponents recognize that the high cost works against the measure, especially in such budget-conscious times, and they say that the Reagan administration is expected to oppose such a wide-ranging and expensive social program. But they point out that the lack of affordable, high-quality child care has become a major concern for a growing number of working couples and single parents and that children's issues have received increased national attention recently.

"The quality {of child care} is so low that children are being abused or neglected. We have to address this," said Rep. Dale E. Kildee (D-Mich.), chairman of the House Education and Labor subcommittee on human resources and principal House sponsor of the legislation.

"I am appalled at the number of disasters and deaths {of children} we are seeing . . . . We are beginning to see the consequences of parents making choices out of desperation," said Helen Blank of the Children's Defense Fund, a member of the coalition.

"We are going to sacrifice a whole generation of children if we wait much longer."

Sen. Christopher J. Dodd (D-Conn.), chairman of the Senate Labor and Human Resources subcommittee on children and the principal Senate sponsor, noted that "it's going to be hard to be talking about that kind of money" but added that there appears to be a consensus on the need for more quality child care.

"I feel pretty optimistic about getting something done" on child care in Congress next year, Dodd said.

The sponsors and advocates are hoping that one major bill, backed by a coalition of more than 80 national organizations, will have a better chance of passage than recent piecemeal approaches.

Congress passed a wide-ranging, $2 billion child care bill in 1971, but it was vetoed by President Nixon, who cited its high cost and "family-weakening implications." At the time, the efforts of labor and welfare groups were widely credited with passage of the legislation by Congress.

Hoping to duplicate that effort, proponents of the current legislation in June announced the formation of a coalition calling itself the Alliance for Better Child Care, which helped draft the comprehensive legislation.

Among the coalition members is the American Federation of State, County and Municipal Employees, the largest AFL-CIO union, which has vowed to put child care "on the top of the 1988 political agenda." The Communications Workers of America, the United Food and Commercial Workers Union and the American Federation of Teachers are also members.

The coalition includes such organizations as the United Way, YMCA, National Education Association, Americans for Democratic Action and a long list of children's welfare and church-sponsored organizations.

The bill would establish the first national standards of quality for child care services. These would include the number of children that one adult could care for at home, staff-to-child ratios at day care centers, day care provider training, and health and safety requirements. Federal funds would be available for training child care workers and for states to monitor compliance with the regulations.

At the state level, where child care regulations have rested so far, standards vary widely. But even where there are stringent standards for child care, government officials estimate that a majority of children in care are in unlicensed situations because enforcement is difficult.

Ideally, one child care worker should care for no more than three infants at a time, according to the National Association for the Education of Young Children.

But only three states (including Maryland) currently limit the number of infants in one person's care to three, the Children's Defense Fund said.

The proposed bill would allow no more than four infants to be cared for by one worker; it would strengthen the standard in 21 states, according to the Children's Defense Fund.