A federal judge in Richmond ordered yesterday that the execution of murderer Wilbert Lee Evans be postponed and that a hearing be scheduled to determine if an Alexandria jury erred when it recommended the death sentence.

U.S. District Judge Robert R. Merhige Jr., citing Evans's role in protecting hostages during a 1984 prison uprising, said in a 14-page opinion that Evans's attorneys have "made a substantial showing that the jury's prediction of a probability of future dangerousness was incorrect."

The jury found that Evans committed capital murder and that he constituted a continuing threat to society, a necessary condition for a death sentence.

Merhige said he will set a date in the next few days to hear evidence on whether Evans's death sentence should be reduced to life in prison.

Evans, 44, was sentenced to die in the electric chair for killing Alexandria deputy William Gene Truesdale during a failed 1981 escape attempt from Alexandria's Old Town jail.

In recent weeks supporters have mounted an aggressive publicity campaign to save Evans, saying he deserves clemency after braving knife-wielding fellow inmates to protect 14 hostages in a death row revolt at the Mecklenburg Correctional Center.

Merhige largely agreed with Evans's lawyers that his role in quelling the prison uprising undercut the jury's finding. "Rather than participate in the disturbance, according to correctional officers held hostage during the uprising, petitioner protected the guards, calmed the violent situation and stopped an inmate from raping a nurse also held hostage," he wrote.

Merhige cited affidavits presented on Evans's behalf by hostages and prison personnel who credited Evans with securing their safety. A former administrator for the state Department of Corrections wrote in a November 1989 letter that Evans assisted the hostages, and that if his death sentence were commuted, it would present "a possible positive effect on future inmate behavior."

Senior Assistant Attorney General Donald R. Curry said the state will appeal Merhige's finding to the 4th U.S. Circuit Court of Appeals. He declined to discuss Merhige's opinion.

Curry had argued in court yesterday morning that if a jury properly imposes a sentence, it cannot be modified by events that occur afterward. He also said that except under exceptional circumstances, a federal court may not interfere with the imposition of state judgments.

Jonathan Shapiro, who has represented Evans for the past eight years, said that because Evans's life was at stake he had asked that the state not appeal the case and allow evidence to be presented on both sides.

"It's the right thing to do," Shapiro said. He added that if Merhige's ruling stands and the hearing is allowed to take place, he will "subpoena all the guards who have talked with us" about Evans's conduct during the Mecklenburg incident.

The case against Evans goes back to January 1981 when Evans, already in custody for assault in North Carolina, was brought to Alexandria to testify at an extradition case against another North Carolina man.

Evidence presented at Evans's trial showed that he was brought back to the Alexandria jail, saw an open gate leading to the street and reached for Truesdale's gun. In the ensuing struggle, Truesdale was fatally shot.

Evans escaped, but was recaptured when police surrounded him in a church parking lot about eight blocks from the jail.

Evans was first sentenced to death in 1981, but the state Attorney General's Office admitted that prosecutors had entered tainted evidence during the sentencing phase of his trial. Evans was sentenced to death a second time in March 1984.