A closely divided U.S. Supreme Court on Wednesday upheld the first nationwide ban on a specific abortion procedure, restricting abortion rights in a ruling on one of the nation's most divisive and politically charged issues.

By a 5-4 vote, the high court rejected two challenges to the Partial-Birth Abortion Ban Act that President George W. Bush signed into law in 2003 after its approval by the Republican-led U.S. Congress.

The decision marked the first time the nation's high court has upheld a federal law banning a specific abortion procedure since its landmark Roe v. Wade ruling in 1973 that women have a basic constitutional right to abortion.

In a defeat for abortion rights advocates, the court's conservative majority with two Bush appointees upheld the law adopted after nine years of hearings and debate. The law has never been enforced because of court challenges.

The majority opinion written by Justice Anthony Kennedy rejected arguments the law must be struck down because it imposes an undue burden on a woman's right to abortion, it is too vague or too broad and fails to provide an exception for abortions to protect the health of a pregnant woman.

The court's four most liberal members -- Justices Ruth Bader Ginsburg, John Paul Stevens, David Souter and Stephen Breyer -- dissented.

Ginsburg, who called the decision alarming, took the rare step of reading parts of her dissent from the bench.

"In candor, the Partial Birth Abortion Act and the court's defense of it cannot be understood as anything other than an effort to chip away at a right declared again and again by this court -- and with increasing comprehension of its centrality to women's lives," she said.

The upheld law makes it a crime for a doctor to perform an abortion when the "entire fetal head" or "any part of the fetal trunk past the navel" is outside the woman's uterus.

The procedure, which often occurs in the second trimester of pregnancy, is known medically as intact dilation and extraction.

The two cases, widely viewed as the most important of the court's 2006-07 term, had been closely watched as tests of whether Bush's two conservative appointees, Chief Justice John Roberts and Justice Samuel Alito, would restrict abortion rights. Both voted to uphold the law.

Roberts and Alito as U.S. Justice Department lawyers in the 1980s and early 1990s opposed the 1973 abortion ruling. Abortion was a central issue in their Senate confirmation hearings, when neither Roberts nor Alito would divulge how he would vote on abortion cases.

Abortion rights advocates who challenged the law denounced the ruling.

"This ruling flies in the face of 30 years of Supreme Court precedent and the best interest of women's health and safety," said Eve Gartner of Planned Parenthood Federation of America.

"Today the court took away an important option for doctors who seek to provide the best and safest care to their patients. This ruling tells women that politicians, not doctors, will make their health care decisions for them," she said.

The Supreme Court by a 5-4 vote in 2000 struck down a similar Nebraska law for failing to provide an exception to protect a pregnant woman's health.

But moderate Justice Sandra Day O'Connor, who cast the decisive vote in 2000, has retired and was replaced by the more conservative Alito.