The federal government must play a major role in providing quality child care or America's competitive edge may be jeopardized, officials of the largest AFL-CIO union and a children's advocacy group warned yesterday.

Jerry McEntee, of the American Federation of State, County and Municipal Employees and Marian Wright Edelman, of the Children's Defense Fund, stressed the need for a national child care policy.

Their plea coincided with the appearance in a local newspaper of a half-page advertisement placed by their organizations asking: "For the sake of America's children ... if not now, when? Child care is the key to a better America."

Edelman and McEntee said lobbying will start later this year to push Congress to support a bill for $2.5 billion in direct federal funding for day care expansions.

Without a national policy, they said, a shrinking workforce and an increased number of children who lack adequate supervision will eventually lead to a decline in America's competitive edge.

Edelman said $1 invested in preschool education returns $4.75 in savings because of lower special education costs, lower welfare costs and higher worker productivity.

By 1995, Edelman said nearly 15 million children will have a mother in the work force, representing a 50 percent increase over the 1985 figure of 9.6 million children.

Young people 16 to 24 years old made up 27 percent of the population in 1978 but by 1995 will account for only 19 percent, she said, noting, "The value of every individual worker increases."

"Yet, our traditional neglect of children, particularly poor children, imperils their futures and our future as a competitive nation," Edelman said.

Among the children needing care, Defense Fund statistics showed, one in four children is poor, one in three is a minority, one in five is at risk of becoming a teen parent, one is six is in a family where neither parent works and one in seven is at risk of dropping out of school.

McEntee added that only 3,000 out of 6 million American employers supported the child care needs of their workers last year.

But, he said a recent national opinion survey by a Boston polling firm found working Americans, by a 53 percent to 26 percent margin, felt child care facilities now are inadequate. Twenty-one percent were uncertain.

Seventy-one percent said the government should develop policies to help make child care services more available and affordable, while 23 percent disagreed and 6 percent were undecided, the poll found.

"AFSCE intends to make child care a major workplace issue of the 1980s and 1990s," McEntee said. "There is no reason why millions of working parents and their children should be the victims of inadequate or stopgap child care which fails to meet their needs."