He was not too frail to kill others!

SAN FRANCISCO, California (AP) -- California's oldest death row inmate -- a 75-year-old who is legally blind and nearly deaf -- is asking the U.S. Supreme Court to do something it has never done before: block an execution because of the condemned man's advanced age and infirmity.

Clarence Ray Allen's attorneys contend that executing a feeble old man amounts to cruel and unusual punishment banned by the U.S. Constitution.

Allen is set to die by injection Tuesday for ordering three slayings while behind bars for another murder. He has been on death row for more than 23 years.

Allen, who turns 76 on the eve of his execution, would be the second-oldest person executed in the United States since the Supreme Court allowed capital punishment to resume in 1976. He often uses a wheelchair and had to be resuscitated after suffering a heart attack last year at San Quentin Prison.

"The spectacle of Mr. Allen being wheeled into the death chamber, unable to walk and unable to see those who have come to witness his execution, violates all standards of decency and would amount to nothing more than the purposeless and needless imposition of pain and suffering prohibited by the Eighth Amendment," said Annette Carnegie, one of Allen's attorneys.

The Supreme Court has said it is cruel and unusual to execute the mentally retarded, those who are so mentally incompetent they do not understand they are about to be executed or why, and inmates who killed when they were juveniles.

But the high court has never stopped an execution because of an inmate's advanced age or physical infirmities.

Sparing Allen could open the way for similar legal challenges from other sickly death row inmates. At the same time, some defense attorneys fear that if Allen prevails, states may restrict death row appeals -- for example, by setting firmer filing deadlines -- to prevent inmates from trying to run out the clock.

Prosecutors are fighting Allen's last-ditch appeal.

"The U.S. Supreme Court has never spoken to an exception to an upper age limit or a physical illness," said prosecutor Ward Campbell. "As a result, there is no case law from the United States Supreme Court compelling the courts to grant a reprieve."

The California Supreme Court denied similar claims by Allen on Tuesday.

The U.S. Supreme Court in 2004 refused to block the execution of James Hubbard, 74, of Alabama despite his claims of advanced age and mental incompetence.

In Mississippi last month, John B. Nixon Sr., 77, became the oldest inmate executed since capital punishment was reinstated in this country. He did not base his appeals on his age.

"We carefully considered it," said his lawyer, Brian Toohey. "There was no case law backing us up." However, Nixon did ask Gov. Haley Barbour for clemency because of his age.

Allen has a similar plea for mercy before Gov. Arnold Schwarzenegger, who has refused to hold a hearing in the case. In his two years in office, Schwarzenegger has denied three petitions for clemency based on claims of innocence, mental incompetence, and good behavior or good deeds in prison.

The brother of one of Allen's victims said the arguments in favor of sparing the killer's life are nonsensical. Robert Rocha -- whose sister, Josephine, was murdered at a Fresno market in 1980 by a hitman Allen hired -- said Allen's repeated appeals are the only reason he is old and frail.

"Mr. Allen feels he is too old to die," Rocha said. "We feel Josephine was too young to die. She was only 17 when she was taken from us and murdered."

Allen was among California's first convicts condemned after the sate's death penalty was reinstated in 1977. He has been on death row since 1982.

Regardless of whether Allen is successful, legal experts predict such claims will be repeated by other condemned inmates, especially in California, where the nation's largest and most backlogged death row has an aging population.

California's death row houses five men older than 70; 34 are ages 60 to 69. Viva Leroy Nash, 90, of Arizona is the nation's oldest death row inmate. No execution date has been set.

The average age of the nation's condemned prisoners is 41, and the average stay on death row is a decade, according to the Bureau of Justice Statistics.