After Elaine Fromm's husband left her when she was eight months pregnant with their fourth child, she could not get local or state officials to require her ex-husband to pay the $7 per week each child was owed for support. She spent the next 12 years -- first on welfare and later working as a secretary -- rearing the children in a slum apartment in Baltimore.

For many of the 4 million women who head households in which child support is unpaid, Fromm's situation is all too common. But a new federal law, effective today, forces states to withhold child support from paychecks after a parent falls a month behind in payments.

"This law would have made a tremendous difference in the horrendous circumstances under which I had to raise my children," said Fromm, who plans to use the law to collect belatedly the unpaid $21,000 in support payments, $9,000 of which is owed to Maryland to reimburse her welfare payments.

Although authorities in South Carolina, where her ex-husband now lives, have not answered her earlier petitions, the new law requires states to cooperate in enforcing support orders, or lose federal funds.

The law, which must be enacted by each state within four months of its current legislative session, puts new emphasis on working and middle-class delinquent parents. The nation's first child-support law, passed in 1975, rewarded states for recovering money for welfare families by returning half of the dollars collected to the states.

"The weight of the state has been on those least able to pay child support, those haunted by unemployment and miserable wages," said Ron Haskins, associate director of the Bush Institute for Child and Family Policy at the University of North Carolina at Chapel Hill. "This new law will be successful if the states believe the new formula pays them well enough to go after the middle-class father."

Under the law, states must attach the wages after a parent who has been ordered by a court to pay child support is 30 days in arrears. States also must attach the state tax refund of delinquent parents and place liens on their property.

States also must impose a security bond on a parent with a history of nonpayment and have the option of telling local credit bureaus of a parent's nonpayment.

"Twenty-two states already have passed laws that meet the federal law," according to Michelle Jefferson, a spokeswoman for the Federal Office of Child Support Enforcement, a Rockville office that operates a system to locate absent parents by checking Social Security records, federal tax returns and military records. The remaining states, including Maryland and Virginia, as well as the District of Columbia, have one or more of the requirements in current laws and must approve the others this year, she said.

"We expect to collect much of the $3 billion that the Census Bureau reported was unpaid in child support [in 1983]," said Jefferson.

The law is expected to help keep families from resorting to welfare. The U.S. Department of Health and Human Services has estimated that almost 87 percent of families on welfare were eligible only because "of a living parent's absence from the home."

In the emotional arena of divorce, the law is not without controversy.

"It will heighten the antagonism," said Jim Cook of Los Angeles, president of the 2,000-member Joint Custody Association. "It will increase the warfare because visitation isn't addressed."

Cook added, "In cases where visitation is not thwarted, we know more support is paid. There need to be restraints on freely moving out of state with a child."

Rep. Barbara Kennelly (D-Conn.), the bill's chief sponsor in the House, noted that governors must set up special child support commissions to deal with visitation and other issues raised by the law. States also are encouraged to set up uniform guidelines on setting support awards and to consider making child support an automatic wage deduction, rather than waiting for delinquencies to develop.

In Virginia, for example, the governor's commission on child support issued a report last week calling for required mediation between divorcing parents and a presumption that custody will be shared. "It's a unanimous recommendation that the state totally revamp the way custody is done after divorce," said Carl Friedman, a computer science professor at the University of the District of Columbia and a member of the Virginia commission.

Adopting such proposals would help eliminate the need for wage withholding, Friedman and others said.

"We think joint custody is the better solution to all these problems," said David Levy, a member of the Maryland governor's commission and president of the National Council for Children's Rights, a D.C. advocacy group for children of divorced parents. "Wage withholding won't work for those without jobs or for those who job-hop or go into the underground economy."

But Fromm, who has since remarried and now directs an advocacy group, The National Organization for the Enforcement of Child Support, from her Reisterstown, Md., home, said the law prevents frustrating and futile attempts to force courts to enforce their orders. Her group has been advising parents to have their court orders modified to give state child enforcement offices the power to collect the payments.

"All these years, I tried to get someone to sue him and no one would bother," she said. "Each time I tracked him down, the most they would send was a form letter and he'd move.

"A lot of parents realized they didn't have to pay because the government would take care of their families," she said. "Now the government is cracking down. It's the greatest present kids in a divorced family could get."