SAN FRANCISCO  Facing sharp questions from a federal appellate panel and concerns about a drug used in lethal injections, a federal judge in California has canceled what would have been California’s first execution in more than four years.

Albert G. Brown Jr., 56, was convicted in 1982 of raping and strangling a 15-year-old girl in Riverside, Calif., two years before and had been scheduled to die by lethal injection Thursday night.

But late Tuesday, Judge Jeremy D. Fogel of Federal District Court in San Jose issued a stay after a three-judge panel of the United States Court of Appeals for the Ninth Circuit ordered him to again consider the case.

The stay came a day after California officials announced that the state’s supply of sodium thiopental, a barbiturate used in executions, was good only until Friday, a revelation that seemed to shock the appellate panel. “It is incredible to think that the deliberative process might be driven by the expiration date of the execution drug,” the panel wrote.