The Supreme Court made clear Tuesday that it will soon decide if it is constitutional to execute mentally retarded killers, substituting a moot North Carolina inmate's case with one from Virginia.

The court's first choice had been the case of Ernest McCarver, but before arguments could be heard North Carolina passed a law banning such executions.

Justices swapped the McCarver case with one involving a Virginia man who robbed and killed an airman.

"Obviously they do want to take a stand on this issue, one way or the other," said Paula Bernstein, spokeswoman for the Death Penalty Information Center.

The North Carolina law was passed in July, four months after the high court stopped McCarver's execution after he had eaten what was supposed to be his last meal. The Supreme Court dismissed McCarver's appeal.

The court decided to consider one of several cases it had been holding pending its McCarver decision.

Daryl Atkins was convicted of murdering an airman in 1996 because he needed money for beer. He was 18 at the time.

The victim, 21-year-old Eric Nesbitt, was kidnapped outside a convenience store and forced to withdraw money from an automatic teller machine. Atkins and an accomplice took Nesbitt to a deserted field and shot him eight times. Nesbitt was stationed at Langley Air Force Base in Hampton, Va.

With Atkins, the court will revisit the question of whether it is unconstitutionally cruel and unusual punishment to execute a person with mental retardation.

McCarver was sentenced to death for the 1987 murder of a cafeteria worker. Prosecutors and defense experts have disagreed over his impairment.

North Carolina enacted a ban on executing the retarded in August. The law may or may not apply to McCarver, but state prosecutors had asked the Supreme Court to dismiss the case as moot.

Eighteen states and the federal government have some kind of ban on those executions.

President Bush has said he opposes executing the retarded.

"We should never execute anybody who is retarded," Bush said in June. "And our court system protects people who don't understand the nature of the crime they committed."

That same month, his brother, Florida Gov. Jeb Bush, signed a ban into law for Florida while Bush's successor in Texas, Gov. Rick Perry, vetoed a similar proposal.

The Death Penalty Information Center said that Texas has executed six retarded defendants since 1982, two of them while President Bush was governor.

Prosecutors have disputed that, contending that the two men put to death during Bush's years as governor both tested higher on some IQ tests.

The cases are McCarver v. North Carolina, 00-8727, and Atkins v. Virginia, 00-8452.