AUSTIN, Texas The Texas legislature approved a bill that would ban the execution of convicted killers who are determined to be mentally retarded.

The bill was approved by both the House of Representatives and the Senate and was then sent to Gov. Rick Perry who has indicated he will wait for a ruling by the U.S. Supreme Court before deciding whether to sign the bill into law.

The nation's highest court is currently considering the case of Texas death row inmate John Paul Penry, 44, who was convicted of a 1979 murder but is said to be mentally sick.

Texas has executed 246 people, far more than any other state, since resuming capital punishment in 1982, six years after the Supreme Court lifted a national ban on the death penalty.

In April Perry signed into law a bill that will give Texas prisoners greater access to publicly funded DNA tests which have led to the release of death row inmates in several states.

But earlier this month the Texas legislature rejected a bill, backed by Perry, that would have allowed juries in capital murder cases to pass a sentence of life in prison without parole.

As the law stands, Texas juries must choose between death or life imprisonment with the possibility of parole after 40 years.

Supporters of the defeated bill argued the third option was needed because juries were likely to choose the death penalty for fear a convicted killer might be freed and kill again.

At present 38 of the 50 U.S. states impose the death penalty. The first federal execution since 1963 is set to take place next month when Oklahoma City bomber Timothy McVeigh is scheduled to be put to death by lethal injection.