SAN FRANCISCO (AP) _ A federal appeals court ruled Tuesday that hanging is constitutional and upheld the death sentence of a man for a 1982 triple murder in Washington state.

The 9th U.S. Circuit Court of Appeals ruled 6-5 that hanging - used as an optional method for current death sentences only by Washington and Montana - does not violate the constitutional ban on cruel and unusual punishment.

When proper procedures are followed, hanging causes ''rapid unconsciousness and death ... within a matter of a few seconds'' and ''does not involve the wanton and unnecessary infliction of pain,'' said the majority opinion by Judge Robert Beezer.

In a scathing dissent, Judge Stephen Reinhardt said the majority had condoned a ''savage and barbaric method of terminating human life'' and understated the risk of slow strangulation or decapitation. He said hanging was reminiscent of Southern lynchings and had been abolished by the rest of the civilized world.

The ruling appears to leave Charles Rodman Campbell with only a final appeal to the U.S. Supreme Court to forestall his execution. If no further stays are issued, he could be executed as early as April, said Assistant Attorney General Paul Weisser.

Washington law requires a condemned prisoner to choose between hanging and lethal injection, and provides hanging as a method for those who make no choice. Campbell has said making a choice would violate his principles.

Campbell was convicted of the throat-slashing murders of Renae Wicklund, her 8-year-old daughter, Shannah, and a neighbor, Barbara Hendrickson, in Clearview, Wash., in April 1982. The two women had testified against him in an earlier trial, in which he was convicted of sexually assaulting Mrs. Wicklund.