The legality of executing mentally retarded people is being challenged before the U.S. Supreme Court this week by a Texas murderer with the mind of a 7-year-old.

The high court Wednesday is scheduled to hear arguments on whether executing Johnny Paul Penry for a 1979 rape-slaying would be "cruel and unusual punishment" banned by the Constitution.A federal appeals court previously rejected Penry's arguments.

The 32-year-old Penry has an IQ estimated at between 50 and 60. His schooling consists of a few days in the first grade, and he was in and out of mental hospitals while growing up near Houston.

"I was abused - treated like a dog. My mother broke my arm about eight times. My left arm is three inches shorter than my right," Penry said in an interview last summer.

Convicted of rape in 1977, he served two years of a five-year prison term. Three months after his release, he was charged with the murder of Pamela Mosely Carpenter, a Livingston housewife who was raped, beaten and fatally stabbed with scissors she was using to make Halloween decorations.

Penry's case is the second within a year to result in Supreme Court review of the Texas capital punishment law, which since 1974 has sent nearly 300 men and women to death row. Since 1976, when the high court allowed capital punishment to resume, 29 men have been put to death in Texas - more than any other state.