When the Supreme Court decides a case, most people assume that's the end of the matter: whatever the court has ordered will happen pretty soon.

For instance, on Feb. 20, the court ruled, 7 to 2, that the Social Security Administration had used a test far tougher than the law prescribed to determine whether low-income children with disabilities were sufficiently impaired to be eligible for federal cash welfare support.

But, four months later, hundreds of thousands of cases involving disabled children, turned down under the rules judged too tough, have not been reopened. Not a single child whose degree of disability was judged too low by SSA before Feb. 20 has received a dollar in retroactive benefits.

Instead, the SSA and the two legal services lawyers who won the case, Jonathan Stein and Richard Weishaupt of Community Legal Services of Philadelphia, are engaged in an acrimonious dispute over how to carry out the ruling in Zebley v. Sullivan.

The Justice Department, meanwhile, has accused Stein and Weishaupt of making "staggering demands" for $13 million to $15 million in compensation for Community Legal Services as part of a plan to carry out the court ruling, "without stating any basis, much less a reasonable one, for doing so." Stein and Weishaupt have countered that Justice has spread around a "distorted, inaccurate and self-serving account" of discussions.

And Sen. John Heinz (R-Pa.) has written Health and Human Services Secretary Louis W. Sullivan expressing his "alarm over the potential destruction of . . . children's disability files by SSA field offices and federal records centers." Heinz said SSA has recently resumed a policy of destroying old records, and there is no apparent exception for cases affected by the Supreme Court's ruling.

SSA said, however, that under its rules no such files could be destroyed.

The dispute illustrates what often happens when the Supreme Court enunciates a large principle, leaving lesser bodies to sort out the details. "Our goal is the same," said Deputy SSA Commissioner Louis D. Enoff. "We want swift and compassionate justice for these deserving children, but so far we have not been able to agree on the method to achieve it."

Weishaupt said one issue is how many children turned down for benefits should have their cases reopened to see if they would have qualified under less-stringent rules. There is no dispute that about 285,000 cases decided since 1983, when Community Legal Services brought the suit, should be reopened. But Stein and Weishaupt also sought to have about 350,000 cases from 1974-83 reopened. Justice has disagreed.

Another issue is finding the people who were turned down. Many have moved. The lawyers claim SSA procedures for finding people are insufficient, a charge disputed by SSA.

Weishaupt also said he wants SSA to use old case files as a base for evidence of a person's condition, but that SSA wants to require people to submit new documents. SSA has said it will use the old files whenever it is to the claimants' advantage.

Then there is the dispute over whether Sullivan should order states to make retroactive Medicaid payments to people whose cases are reconsidered. Weishaupt argues the lost Medicaid benefits should be restored, but he said the government asserts it does not have authority to order states to make such payments.

As for the $15 million that the Justice Department says Community Legal Services wants, Weishaupt said it is not seeking the money for itself but aims to have the money distributed to legal service groups all over the country for work on disability cases.

He said his group seeks $1.2 million to cover the cost of bringing the Zebley lawsuit and $1.035 million over three years to set up a toll-free phone line for advice and for referral to local lawyers.

"People think that when the Supreme Court rules that you've waved a magic wand and it's all over. But it's not over," said Weishaupt.