Washington - The Supreme Court ruled, 5 to 4, on Wednesday that sentencing someone to death for raping a child is unconstitutional, assuming that the victim is not killed.

    "The death penalty is not a proportional punishment for the rape of a child," Justice Anthony M. Kennedy wrote for the court. He was joined by Justices John Paul Stevens, David H. Souter, Ruth Bader Ginsburg and Stephen G. Breyer.

    The dissenters were Chief Justice John G. Roberts Jr. and Justices Antonin Scalia, Clarence Thomas and Samuel A. Alito Jr., generally regarded as the conservative wing of the tribunal.

    Not since 1964 has anyone been executed in the United States for a crime other than murder, and of about 3,300 inmates now on death row, only two are facing execution for an offense that did not involve a killing - and both of those inmates are in Louisiana. Patrick Kennedy, was sentenced to death for the rape of his 8-year-old stepdaughter and the other is Richard Davis, who was condemned for assaulting a 5-year-old girl.

    The case of Kennedy v. Louisiana, No. 07-343, was the latest in a series in which the justices have weighed particular applications of capital punishment. In 2002, for instance, the Supreme Court barred the execution of mentally retarded defendants, and in 2005 it banned the execution of people for crimes they committed before they were 18.

    But, as Chief Justice Roberts observed when Kennedy v. Louisiana was argued on April 16: "This is quite different. It is focused on the nature of the offense." Indeed, a theme that ran through the argument was that, while the death penalty is a punishment like no other, the rape of a child is a crime like no other.

    In 1977, the Supreme Court banned death sentences for rape. But the victim in that case, Coker v. Georgia, was a young married woman, and the ruling did not specifically discuss the rape of a child. Over the past 13 years, several states have reacted to public outrage over crimes against children by amending their statutes to make the rape of a child punishable by death.

    Louisiana was the first state to do so, amending its death-penalty law in 1995 to include rape of a child under the age of 12. But unlike Louisiana, the other states with similar provisions (Georgia, Montana, Oklahoma, South Carolina and Texas) generally limit the death penalty to defendants previously convicted of sex crimes against children.

    Mr. Kennedy's lawyer, Jeffrey L. Fisher, argued before the justices that it was "at odds with national values" for the state to execute his client, who had never committed such a crime before.

    But Justice Scalia pressed Mr. Fisher on that assertion, noting that the recent trend has been "more and more states permitting the capital punishment" for the rape of a child.

    As for the case at hand, Juliet L. Clark, an assistant district attorney from Gretna, La., countered that Mr. Kennedy, who weighs 300 pounds, had committed "a very savage rape" that caused serious injuries to his victim. And R. Ted Cruz, the Solicitor General for the State of Texas, who argued as a "friend of the court" on the side of Louisiana, said that Mr. Kennedy (like Mr. Davis, the other child-rape defendant on Louisiana's death row) had "committed crimes that are just unspeakable."

    Responding to a question from Justice Ginsburg, Ms. Clark said the Louisiana child-rape law could apply regardless of the sex of the criminal or that of the victim.

    And in support of her argument that crimes against children have long been viewed with special revulsion, and as deserving of special punishment, Ms. Clark pointed out that the Supreme Court ruled in 1990 that states can make it a crime to possess child pornography even in one's home.

    That ruling, in Osborne v. Ohio, carved out an exception to a 1969 Supreme Court ruling that the Constitution protects the possession of obscene material in the privacy of one's residence. Justice Byron R. White wrote for the 6-to-3 majority in the Osborne case, reasoning that Ohio was justified in trying to "destroy a market for the exploitative use of children."

    Of the current Supreme Court, only Justices Scalia, Kennedy and Stevens took part in the 1990 Osborne decision. Justices Scalia and Kennedy were in the majority; Justice Stevens joined with Justices William J. Brennan Jr. and Thurgood Marshall in finding the Ohio law to be unconstitutionally broad.

    For the Supreme Court decision, click here.