"The law need not give abortion doctors unfettered choice in the course of their medical practice,'' Kennedy said in the majority opinion. As long as the law does not impose an "undue burden,'' he said, the government may "bar certain procedures and substitute others, all in furtherance of its legitimate interests in regulating the medical profession in order to promote respect for life, including life of the unborn.''

Kennedy said Congress was entitled to conclude that a certain type of abortion "implicates additional ethical and moral concerns that justify a special prohibition.'' The law is a reasonable measure to encourage women to give birth rather than undergoing such abortions, while also encouraging doctors to "find different and less-shocking methods,'' Kennedy said.

He was joined by the two Bush appointees, Chief Justice John Roberts and Justice Samuel Alito, and by Thomas and Scalia. Alito was appointed by Bush last year to replace O'Connor.

Dissenters were led by Justice Ruth Bader Ginsburg, the court's only woman. She called the ruling an "alarming'' retreat from earlier decisions that had required abortion restrictions to contain exceptions to protect a pregnant woman's health.

"The court deprives women of the right to make an autonomous choice, even at the expense of their own safety,'' said Ginsburg, joined by Justices John Paul Stevens, David Souter and Stephen Breyer. "This way of thinking reflects ancient notions about women's place in the family and under the Constitution.''

The dissenters also said the alternative methods mentioned by the majority were all potentially more dangerous than the banned procedure. They included an injection that would kill the fetus in the womb, or a vacuum-like induction that requires hospitalization.

The justices' opinions are available online at www.supremecourtus.gov/opinions...-380.pdf.