WASHINGTON (AP) — When the Supreme Court last considered executions of the mentally retarded, only two states banned the practice. Now, 18 states prohibit it, and that math will weigh on the court as it reconsiders the issue and the fate of a condemned man with an IQ of 59.

The court debated Wednesday how much public standards have changed since 1989, when the court upheld those executions on a 5-4 vote.

Justice Sandra Day O'Connor wrote then that there was "insufficient evidence of a national consensus" against the executions to determine that they were unconstitutionally cruel and unusual punishment.

That question has been settled, the lawyer for convicted Virginia killer Daryl Renard Atkins told the court.

"What is your definition of consensus?" asked Chief Justice William H. Rehnquist, a question repeated later by other court members. "How many states out of the 50 do you need for a consensus?"

Attorney James Ellis didn't provide a number, but he said there are clear moral concerns about putting to death mentally retarded killers. They should be punished, just not by death, he said.

Twelve states do not execute any murderers and 18 others don't use their death penalties for the retarded.

"That's a super majority," said Justice Ruth Bader Ginsburg.

"We have to be very careful about finding a new consensus. We can't go back," Justice Antonin Scalia said.

President Bush has said he opposes executing the mentally retarded. Texas does not have a ban, and the state executed two retarded defendants while he was governor, according to the Death Penalty Information Center. Prosecutors have disputed the IQs of some executed Texas inmates.

Pamela A. Rumpz, a Virginia assistant attorney general, told justices that public opinion would change overnight if Osama bin Laden was captured, brought to America for trial and argued that he was mentally retarded.

She also said that the death penalty is appropriate for people like Atkins, convicted of killing an airman in Virginia. Atkins, who was 18 at the time, had more than 20 previous felonies and was aware of his wrongdoing, she said.

"We're not looking at somebody whose culpability is any less than yours or mine," Rumpz told justices.

Justice Stephen Breyer said there are defendants with low IQs who have a hard time functioning. "Maybe they are not so culpable as you or me," he said.

Justice David H. Souter asked if it was also appropriate to execute 5-year-olds.

Atkins has an IQ of 59, considered mildly mentally retarded. People who test 70 or below generally are considered mentally retarded.

There are more than 3,700 people on death row. None of the attorneys could say Wednesday how many of those might be retarded. Other groups have said anywhere from 10 percent to 25 percent of death row inmates could have low IQs.

It's estimated that about 1 percent of the general population is mentally retarded.

Scalia said that even without restrictions, juries can now decide whether someone is "not playing with a full deck" and shouldn't be put to death.

But Ellis argued that mental retardation would more likely work against a defendant, and jurors could use that to justify a tougher penalty.

Ellis did not know how many states have executed mentally retarded defendants since 1989. Breyer said by his count, that number may be only two or three states.

O'Connor, who could be a swing vote in what is expected to be a close ruling, noted that if the executions are declared unconstitutional, states could make their own rules for determining who is retarded.

In addition to Georgia, Maryland and the federal government, which had bans in 1989, new laws were added in Arizona, Arkansas, Colorado, Connecticut, Florida, Indiana, Kansas, Kentucky, Missouri, Nebraska, New Mexico, New York, North Carolina, South Dakota, Tennessee, and Washington.

Virginia's Legislature debated a ban, but decided to await the outcome of this case. The court should rule before July.

The victim in the case, 21-year-old Eric Nesbitt, was stationed at Langley Air Force Base in Hampton, Va.

The case is Atkins v. Virginia, 00-8452.