ASHINGTON, Dec. 1 — The Supreme Court agreed on Monday to decide whether its decision that overturned the death penalty laws of five states 18 months ago should be applied retroactively. If the answer is yes, more than 100 death-row inmates in five states will be entitled to new sentencing hearings.

In Ring v. Arizona, decided in June 2002, the court held that juries rather than judges had to make the crucial factual determinations that separated convicted murderers eligible to be sentenced to death from those who were not. While juries in most states have the role of determining the existence of "aggravating factors," five states — Colorado, Idaho, Montana and Nebraska, in addition to Arizona — gave that role to judges.

Inmates in those states with cases still on appeal received new sentencing hearings, and the states have changed their laws to conform to the Ring decision. The question for the Supreme Court now is whether inmates who have exhausted their direct appeals in state courts can bring habeas corpus petitions in federal courts to challenge the constitutionality of their death sentences.

Underlying that question is one that the new case, also from Arizona, does not directly raise, the retroactivity of the Supreme Court decision three years ago in Apprendi v. New Jersey that ushered in what has amounted to a revolution in criminal sentencing. That ruling, which led directly to the Ring decision, held that juries, and not judges, have to determine any fact that increases a sentence above the statutory minimum. Both decisions were based on the Sixth Amendment right to trial by jury.

Sorting out the implications of that decision, which overturned a hate-crime statute in New Jersey, has proved a daunting task for the entire criminal justice system. The Supreme Court itself has already decided several follow-up cases, and had earlier this term scheduled another new one, Blakeley v. Washington, on the implications of the Apprendi and Ring decisions for states' sentencing-guideline systems.

But the court has never said whether the Apprendi ruling is retroactive. If the Ring decision — a kind of "son of Apprendi" — is determined to be retroactive, logic would suggest that the Apprendi ruling itself is retroactive, as well, an outcome that would be even more unsettling.

The new case, Schriro v. Summerlin, No. 03-526, is an appeal by the State of Arizona from a ruling in September by the United States Court of Appeals for the Ninth Circuit, in San Francisco. The appeals court adopted two alternative theories for applying the Ring decision retroactively.

Supreme Court precedents strongly disfavoring the retroactive application of new constitutional interpretations, along with the restrictive approach to habeas corpus in a 1996 federal law, have made the retroactivity question an elusive and technically difficult one. Essentially, a ruling must make a substantive rather than merely procedural change in the law, or if it is procedural, it must make such a drastic change as to be considered a "watershed." The Ninth Circuit found the Ring decision to meet each of these tests.

The Arizona inmate whose death sentence is directly at stake, Warren W. Summerlin, was found guilty in 1982 of sexually assaulting and murdering a bill collector who had arrived at his home. The judge at his trial sentenced him to death after finding two aggravating factors, that Mr. Summerlin had a previous conviction for a violent felony and that he committed the new offense in an "especially heinous, cruel or depraved manner." Those are findings that under the Ring decision only a jury can make. His sentence was affirmed on appeal in the state courts, and his federal habeas corpus appeal was pending when the Supreme Court issued the Ring decision.

These were among the other developments on a busy Monday at the court.

Jury Challenges

Seventeen years after ruling that peremptory jury challenges could not be used in a racially discriminatory manner, the court agreed to settle a dispute over how such cases should proceed. The question is what amount of evidence suggesting an impermissible racial motive has to be shown for the judge to require an explanation of why certain prospective jurors were removed from the panel.

In Batson v. Kentucky, the 1986 decision that established a new framework for objecting to peremptory challenges, the Supreme Court said that the party making the objection had to raise "an inference of discriminatory purpose." At that point, the side that removed the jurors has to provide a nonracial explanation.

The California Supreme Court, however, has developed its own test, requiring a showing of a "strong likelihood" of racial bias, which it has defined as "more likely than not." While the California court maintains that this test is consistent with the Supreme Court's test in the Batson decision, the Ninth Circuit, which hears federal appeals in California, has found it "impermissibly stringent" and has refused to defer to state court rulings on the question.

The Supreme Court accepted an appeal by a California inmate, Jay S. Johnson, a black man who was convicted of murdering a white child. He was tried by an all-white jury after the prosecution had used its peremptory challenges to remove all three black potential jurors. The California Supreme Court ruled that Mr. Johnson had not made a sufficient showing of racial bias.

While defending that decision, the California attorney general's office urged the justices to hear Mr. Johnson's appeal in an effort to resolve the confusion over handling such cases. The case is Johnson v. California, No. 03-6539.

Gun Rights

In another California case, the justices refused without comment to hear a challenge to the state's 1999 ban on assault weapons. The nine California residents who brought the case, Silveira v. Lockyer, No. 03-51, tried to use it as a vehicle for the Supreme Court to reconsider its longstanding position that the Second Amendment does not protect an individual right to own firearms that are not connected to the collective defense operations of a state militia.

The case had been closely watched in light of Attorney General John Ashcroft's embrace of the National Rifle Association's position on the Second Amendment. While the federal appeals court in New Orleans also endorsed the individual rights theory last year, the Ninth Circuit in this case rejected it over several spirited dissents.

Pledge of Allegiance

The justices granted permission to Dr. Michael A. Newdow, the California father who sued to keep the Pledge of Allegiance from being recited in his daughter's classroom, to argue his own case when the court hears the school district's appeal this winter. Dr. Newdow, who is a lawyer as well as a medical doctor, needed the court's permission because he does not meet the requirements for membership in the Supreme Court bar.

To be eligible, a lawyer must have been a member of the bar of the highest court in a state for at least three years. Dr. Newdow has been licensed to practice law in California only since last year. As a lawyer arguing his own case, he will have an even greater stake than usual, because a preliminary question to be decided is whether as the noncustodial parent he had standing to file the case asserting his daughter's right not to hear "under God" in the daily recitation of the pledge.