A three-judge panel of the U.S. 9th Circuit Court of Appeals in San Francisco issued a stay for triple murderer Charles R. Campbell, 34, who had been scheduled Thursday to become the first person executed by hanging in the nation since 1965. The court granted the stay pending its ruling on his appeal and ordered additional briefs submitted by June 21. Campbell had been sentenced to die at Washington State Penitentiary in Walla Walla for the 1982 revenge killings of Renae Wicklund, 31, her 8-year-old daughter, Shannah, and a neighbor, Barbara Hendrickson, 51, whose throats were slashed in the small town of Clearview, Wash., about 20 miles northeast of Seattle. The three were slain when Campbell was on work release from a prison sentence for a 1976 sexual assault on Wicklund. Both she and Hendrickson had testified at his 1978 trial.