The decision heralds a more receptive approach toward abortion restrictions from a court that in 2000 overturned a similar Nebraska law. Bush's appointees, Chief Justice John Roberts and Justice Samuel Alito, helped turn the tide in today's case, joining Justices Anthony Kennedy, Antonin Scalia and Clarence Thomas.

The court stopped short of overruling the 2000 case, Stenberg v. Carhart, saying the federal statute was narrower in key respects than the Nebraska law. The majority also left open the possibility that doctors could ask a judge for permission to use the disputed procedure for particular medical conditions that pose a health risk to the mother.

The law, which has never taken effect, is the first federal abortion restriction since the landmark 1973 Roe v. Wade decision established the constitutional right to end a pregnancy. The case didn't challenge the validity of Roe.

The measure outlaws procedures in which a fetus is partially removed from the mother before being killed. Although the law is aimed primarily at a procedure known as intact dilation and extraction, or intact D&E, critics faulted the statute for not tracking the medical definition of that technique.

Intact D&E is a relatively rare technique used by some doctors in the second trimester of pregnancy. The vast majority of U.S. abortions are performed during the first trimester.

In signing the measure into law in 2003, Bush said that "a terrible form of violence has been directed against children who are inches from birth." Doctors who violated the law face as much as two years in prison.

Justices Ruth Bader Ginsburg, Stephen Breyer, John Paul Stevens and David Souter dissented.

The cases are Gonzales v. Carhart, 05-380, and Gonzales v. Planned Parenthood, 05-1382.