The Supreme Court on Monday refused to reinstate the Iran-Contra convictions of former national security adviser John M. Poindexter.

The court, without comment, let stand an appeals court ruling that said Poindexter's immunized testimony to Congress improperly was used against him.In throwing out Poindexter's criminal convictions, the appeals court also ruled too vague the federal obstruction law used to prosecute him for allegedly lying to Congress.

Poindexter was convicted in April 1990 of covering up the Iran-Contra affair. He was found guilty of conspiracy, obstructing Congress and false statements.

Poindexter had been sentenced to six months in jail and a $250 fine before his convictions were overturned by the U.S. Circuit Court of Appeals for the District of Columbia last year.

Poindexter and his aide, Oliver North, were central figures in the Reagan-era scandal over secret arms sales to Iran and the diversion of profits to aid Nicaragua's Contra rebels.

The scandal also haunted President Bush, and new questions about how much he knew of the arms-for-hostages swap were raised just days before the Nov. 3 election.

Poindexter testified at publicized congressional hearings in 1987 under a limited grant of immunity. He did not testify at his own trial.

But North was called as a witness and said he could not be sure whether his recollections had been influenced by Poindexter's immunized testimony.

All charges against North were dismissed in September 1991 after independent counsel Lawrence Walsh gave up trying to prove that witnesses were not influenced by North's immunized testimony to Congress.

The appeals court two months later reversed Poindexter's convictions. It ordered the case returned to a trial judge but said the charges had to be dismissed if prosecutors could not prove Poindexter's trial was untainted by his congressional testimony.

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The court also:

- Upheld new districts for the New York Assembly, rejecting arguments that they unfairly dilute Republican voting strength. Critics said the plan signed in May by Gov. Mario Cuomo was an illegal gerrymander.

- Agreed to decide whether homeowners seeking to reorganize debts in bankruptcy court may avoid repaying their full mortgage debt if it exceeds their home's value. The court said it would hear an appeal by a Dallas couple who owed about $71,000 on a condominium valued at $23,500.

- Steered clear of a Florida case involving the rap group 2 Live Crew. Their album "As Nasty as They Wanna Be" was found obscene in 1990, but that was reversed on appeal. The Supreme Court refused to consider a sheriff's effort to get the conviction reinstated.