The Supreme Court ruled yesterday that its 2002 decision requiring juries rather than judges to decide between life imprisonment and the death penalty does not apply retroactively, clearing the way for the eventual execution of more than 100 death row inmates in four states.

By a vote of 5 to 4, the court said that its ruling two years ago in Ring v. Arizona was not such a fundamentally new rule of law that its benefits should flow to everyone, including those whose death sentences became final before then. In Ring, the court held that state laws assigning judges the power to find "aggravating factors" that warrant capital punishment violated the Sixth Amendment guarantee of a trial by jury.

"The right to jury trial is fundamental to our system of criminal procedure and States are bound to enforce the Sixth Amendment's guarantees as we interpret it," Justice Antonin Scalia wrote in the opinion for the court. "But it does not follow that, when a criminal defendant has had a full trial and one round of appeals in which the State faithfully applied the Constitution as we understood it at the time, he may nevertheless continue to litigate in hopes that we will one day have a change of heart."

Scalia was joined by Chief Justice William H. Rehnquist and Justices Sandra Day O'Connor, Anthony M. Kennedy and Clarence Thomas.

The case, Schriro v. Summerlin, No. 03-526, had the potential to overturn 111 death sentences in four states: 87 in Arizona, 15 in Idaho, five in Montana and four in Nebraska. That would have eliminated more than two-thirds of those states' total death row population of 161, forcing the states to choose between settling for life imprisonment and spending millions of dollars to conduct new sentencing hearings in front of juries.

It could also have changed 15 Nevada cases in which offenders were sentenced to death under a law that let judges decide sentences when juries deadlocked or defendants pleaded guilty.

Under a 1989 Supreme Court ruling that limited capital defendants' constitutional appeals, only those relatively rare Supreme Court decisions deemed to have revolutionized constitutional law can be applied retroactively.

Last year, the U.S. Court of Appeals for the 9th Circuit, based in San Francisco, ruled that Ring qualified under this standard. That court also observed that a trial by jury would enhance the fairness and accuracy of the sentencing process.

The defendant in yesterday's case, Warren W. Summerlin, was sentenced to death on July 12, 1982, for the rape and murder of a debt collector. The Arizona judge who sentenced him was later disbarred, after he admitted he had been a habitual marijuana user during the time he decided Summerlin's fate.

Recent research by Cornell University professors John Blume, Theodore Eisenberg and Martin T. Wells found that 4 percent of convicted murderers in single-judge-sentencing states were sentenced to death in recent decades, in contrast to 2 percent of convicted murderers in jury-sentencing states.

But Scalia said that Ring was not a "watershed" because it changed the decision maker in capital cases, not the definition of capital murder. He added that "the evidence is simply too equivocal" to conclude that juries are more accurate fact finders than judges.

Justice Stephen G. Breyer dissented, joined by Justices John Paul Stevens, David H. Souter and Ruth Bader Ginsburg.

Breyer lamented the fact that the court's decision permits the execution of some death row inmates sentenced in trials the court would not approve today.

The "ordinary citizen," he wrote, "will simply witness two individuals, both sentenced through the use of unconstitutional procedures, one individual going to his death, the other saved, all through an accident of timing."

But Arizona and the other states whose systems of capital punishment were at issue say they were being whipsawed by changing court rulings.

Arizona enacted its judge-only death-sentencing statute in 1973, in an effort to comply with a 1972 Supreme Court ruling that struck down all state capital punishment laws as arbitrary. It was upheld by the Supreme Court in 1990 before being struck down in Ring.