ATLANTA (Reuters) A federal judge refused late on Tuesday to issue a stay of execution for a man who claimed Georgia's supply of lethal injection drug sodium thiopental has "almost certainly" expired, meaning he would be subjected to an unnecessarily painful death.

In his ruling, Judge Timothy C. Batten held inmate Roy Willard Blankenship failed to prove his claims Georgia's supply of the drug has expired.

"Even if Blankenship could show that it was sure or very likely that the sodium pentothal has expired, he has failed to show that the expired drug is less effective and that its use will therefore cause him to needlessly suffer," Batten also ruled.

Georgia claims its stockpile of the drug does not expire until 2014.

Blankenship, sentenced to death for the 1978 murder and rape of a 78-year-old woman, had been scheduled for execution by lethal injection February 9 but the Georgia Board of Pardons and Paroles issued a stay through February 17.

Sodium thiopental has been in short supply nationally after the only U.S. company that manufactured the drug halted production because it does not want it to be used in executions.

(Reporting by David Beasley; Editing by Jerry Norton)