MORRISVILLE, PA. -- The case of John Pozsgai, the Morrisville mechanic whose conviction for filling a wetland made him the most punished American for an environmental crime, has taken another curious turn.

In a brief opposing Pozsgai's appeal of his 1988 federal court conviction and sentence, filed last week in the Supreme Court, Solicitor General Kenneth W. Starr conceded that the trial record proving the government had jurisdiction over Pozsgai's property was "admittedly quite thin."

In addition, Starr wrote, the brief filed by the government when the case went before the 3rd U.S. Circuit Court of Appeals inaccurately stated that photographs introduced during the trial proved a key legal point that the government had jurisdiction over Pozsgai's property.

Although Starr argues that the faults are not fatal to the prosecution's case, lawyers for Pozsgai this week described Starr's admissions as a vindication. Paul D. Kamenar, executive legal director of the Washington Legal Foundation, a conservative law center that has handled Pozsgai's appeal, noted he had raised the jurisdiction question shortly after Pozsgai was sentenced in July 1989.

Kamenar said he hopes Starr's brief will help him persuade the high court to accept Pozsgai's case for review or return it to the circuit court for a rehearing.

Seth Weber, the assistant U.S. attorney who prosecuted the case, said Justice Department guidelines prohibited him from commenting on a case before the Supreme Court.

Pozsgai, a 58-year-old Hungarian immigrant, was convicted by a federal jury on 40 counts of violating the federal Clean Water Act for filling in about five acres of a 14-acre tract he had bought in hopes of expanding his diesel repair business. He was sentenced by U.S. District Judge Marvin Katz in Philadelphia to three years' imprisonment, a $202,000 fine and restoration of the wetland he filled. Pozsgai remains free pending resolution of his appeal.