At least 82 death row inmates are seeking reprieves in states that recently banned executing the mentally retarded, an inkling of the hundreds who would likely challenge their sentences if the U.S. Supreme Court finds such executions are unconstitutional.

That means roughly one in 10 inmates sought to get off death row because of mental retardation in states where that option became available last year. Some who seek a national ban say the real number of retarded inmates nationally could be twice that, or 20 percent.

Prosecutors say the system already keeps the mentally retarded off death row, and argue a flat-out ban would spur a slew of groundless appeals.

At the murky intersection where the mentally retarded meet the criminal justice system, advocates and prosecutors square off with much unknown how many retarded people are caught in the system and whether they fare worse with police or judges than others.

What seems obvious is that if the high court’s decision creates a ban, hundreds of cases will be headed back to court.

With 2,455 inmates on death row in the 20 states that allow executions of the mentally retarded, that would mean 245 potential challenges if 10 percent sought reprieves. Nationally, there were just over 3,700 condemned inmates at the beginning of 2002.

The states that prohibit executions of the mentally retarded have jumped from two to 18 since the court’s 1989 decision permitting such executions, and at least six more are now considering bans.

In five states that banned such executions last year, at least 82 new challenges have been or will soon be filed claiming mental retardation, defense attorneys estimate conservatively. With a total of 822 death row inmates in those states, that’s one in 10.

Nearly half the claims came in North Carolina, the only state that made the ban retroactive so those already condemned to death could seek a reprieve.

Elsewhere, defense attorneys estimated there were, or would be, at least 28 claims in Florida, 12 in Arizona, two in Missouri and none in Connecticut.

Mental retardation is a condition defined by significantly diminished intellectual ability, usually determined by IQs of about 70 (100 is average); problems with adaptive behavior like holding a job or caring for oneself; and the appearance of symptoms or diagnosis as a child.

Prosecutors in the 20 states that allow such executions say enough safeguards already exist to protect the retarded. In less clear-cut cases, a murderer with low intelligence and poor social skills still deserves punishment, they say.

Advocates for the mentally retarded say executions are unconstitutional because the condition leaves the retarded unable to negotiate police interrogations or court proceedings, and more likely to be wrongfully convicted.

“There’s lots of reasons we shouldn’t execute a mentally retarded person,” said Sean O’Brien, who runs a death penalty clinic at the University of Missouri at Kansas City. “They’re the same reasons we shouldn’t execute a child” even if they committed a horrible crime.