By David Beasley

ATLANTA, Feb 19 (Reuters) - A Georgia man convicted of killing two people and described by his attorneys as mentally disabled was granted last-minute stays of execution on Tuesday by a U.S. federal appeals court and a state appeals court, his lawyer said.

Warren Lee Hill, 52, was scheduled to be executed on Tuesday night for beating a fellow inmate in 1990 to death while serving a life sentence for fatally shooting his girlfriend.

Brian Kammer, one of Hill's attorneys, said the execution would be temporarily halted after the stays granted by the 11th Circuit Court of Appeals and the Georgia Court of Appeals.

The federal court decision came in response to appeals by Hill's lawyers arguing he is mentally retarded, Kammer said. The decision by the Georgia state court followed a legal challenge over the state's method of executing Hill by lethal injection, he said.

"We are greatly relieved that the Eleventh Circuit Court of Appeals has stayed the execution of Warren Hill, a person with mental retardation," Kammer said in an emailed statement.

"All the doctors who have examined Mr. Hill are unanimous in their diagnosis of mental retardation," he said.

In 1988, Georgia became the first U.S. state to enact a law banning the execution of mentally retarded defendants. But according to death penalty experts, Georgia has perhaps the toughest standard in the nation for defining mental retardation, requiring proof "beyond a reasonable doubt."

Mental retardation is generally defined as having a score of 70 or below on intelligence tests, supporters of Hill argue. According to court records, Hill scored 69 on one intelligence test and in the 70s in other examinations.

Last week, Kammer filed affidavits in a Georgia court by three doctors who evaluated Hill for the state 13 years ago and now believe after further review that he is mentally retarded.

"There is now unanimous consensus among all experts who have evaluated Mr. Hill over the last 22 years," Kammer told Reuters on Monday. "Mr. Hill should be deemed to have met Georgia's uniquely stringent burden of proof for proving mental retardation."

However, in court documents, the state of Georgia said the three state doctors reviewed "extensive materials" before concluding in 2000 that he was not mentally disabled, and were thoroughly cross-examined by Hill's attorneys at the time.

The doctors noted in 2000 that Hill had been a recruiter for the U.S. Navy, budgeted his money and was a "father figure" for his siblings, the state said in court documents.

In the new affidavits, one doctor called the earlier evaluation of Hill "extremely and unusually rushed" while another said his opinions of Hill in 2000 were "unreliable because of my lack of experience at the time."

A third doctor cited "advances in the understanding of mental retardation" since 2000 as a reason for changing his findings.

Follow us on Twitter @ReutersLegal | Like us on Facebook