A multiple killer and career criminal who asked to ''die with dignity'' was executed early today for killing a drifter.

The 52-year-old killer, William Paul Thompson, who also asked for forgiveness from his family and from families of three and possibly six murder victims, was given a lethal injection at 2:01 A.M. and pronounced dead eight minutes later.

He was the third person to be put to death in Nevada and the 112th to be executed in the United States since the Supreme Court allowed reinstatement of the death penalty in 1976. Seven other convicted murderers have also been executed so far this year.

The 300-pound inmate spoke briefly with the five guards who helped to hoist him onto a gurney in the prison's old gas chamber, where the lethal injections are now administered, while 25 witnesses and reporters watched.

He was sentenced to die for the 1984 killing of Randy Waldron, a 28-year-old drifter, in Reno. After that sentence, he was convicted of killing two brothers who were camping near Auburn, Calif.

Mr. Thompson said Mr. Waldron ''just got in my way'' while he was on the run from the killings of the brothers. He said he shot the brothers because they were drug informers.

Mr. Thompson said he killed three other men, including a Federal prosecutor in Oklahoma in 1983 whom he was paid to murder. But in Tulsa, United States Attorney Tony Graham said he was not aware of any prosecutor in the state who had disappeared or was killed in 1983. Mr. Graham said he did not intend to investigate Mr. Thompson's claim.

The other murders were in New York and in Kansas, Mr. Thompson said, but he would not name the victims.

The prison warden, Pete Demosthenes, said Mr. Thompson's last words when guards closed the death chamber door were, ''Thank you for letting me die with dignity.''

In the only interview he granted, Mr. Thompson told The Associated Press on Saturday that he had recently found religion and was ''paying back to society the only thing I have to offer it.''