WASHINGTON – The U.S. Supreme Court refused to question the drug combination used in most of the nation’s lethal injections, turning away an appeal by a Tennessee death-row inmate who says he risks suffering “extraordinary pain.”

The court, without comment, yesterday let stand a Tennessee Supreme Court decision that said the state’s procedures don’t violate the constitutional ban on cruel and unusual punishments.

“Subjecting an inmate to such unnecessary pain violates human dignity, which is the very foundation of the prohibition against cruel and unusual punishments,” the inmate, Abu-Ali Abdur’Rahman, argued in court papers filed in Washington.

In turning away the case, the high court passed up a chance to address an increasingly contentious issue that has arisen in at least a dozen cases since 2004. America has averaged 69 executions a year over the last decade, according to the Death Penalty Information Center in Washington.

All but one of the 38 death-penalty states use lethal injections and 35 use the same three chemicals as Tennessee, according to court papers. Nebraska’s method is the electric chair, although the state hasn’t executed anyone since 1997.

The justices are reviewing a separate case that asks whether inmates can use a federal civil rights law to challenge lethal-injection methods. That case is scheduled for decision by the end of June.

Tennessee inmates are first injected with sodium pentothal, an anesthetic, followed by pancuronium bromide, which causes the lungs to shut down and paralyzes the body.The final chemical, potassium chloride, then induces a fatal heart attack.

“The evidence demonstrates that the risk that a condemned inmate will actually experience pain and suffering as a result of Tennessee’s lethal injec tion protocol is less than remote,” the Tennessee attorney general, Paul Summers, argued in papers that urged the Supreme Court not to hear the case.

Abdur’Rahman contended in his appeal that the first chemical might not render him unconscious. If that were to occur, he said, he would be able to feel the effects of the pancuronium bromide, which would freeze his muscles while leaving him able to experience pain and fear.

Death penalty opponents say pancuronium bromide, also known as Pavulon, is so problematic that American Veterinary Medical Association guidelines ban its use in euthanizing animals.

Abdur’Rahman said the warden of the Nashville prison where Tennessee conducts executions, Ricky Bell, adopted the drug combination simply by copying methods used elsewhere without soliciting any medical or scientific advice.

The appeal said Tennessee could eliminate the risks by instead administering only pentobarbital, a longer-acting barbiturate that Abdur’Rahman said is the most common method of euthanizing domesticated animals.

Abdur’Rahman, 55, was sentenced to death for fatally stabbing a drug dealer in 1986. No execution date has been set for him.

The case is Abdur’Rahman v.Bredesen, 05-1036.