WASHINGTON -- In another blow to the Bush administration, the Supreme Court ruled Thursday that foreign terrorism suspects held at Guantánamo Bay have the constitutional right to challenge their detention in U.S. civilian courts.

The 5-4 ruling was the high court's third setback for the administration since 2004 over its treatment of prisoners held indefinitely and without charges at the U.S. naval base in Cuba.

''The laws and Constitution are designed to survive, and remain in force, in extraordinary times,'' Justice Anthony Kennedy wrote for the majority.

It was not immediately clear whether this ruling, unlike the first two, would lead to prompt hearings for the detainees, some of whom have been held more than six years. Roughly 270 men remain at the island prison, classified as enemy combatants and held on suspicion of terrorism or links to al Qaeda and the Taliban.

The Guantánamo prison has been harshly criticized at home and abroad for the detentions themselves as well as the aggressive interrogations that were conducted there.

The court said not only that the detainees have rights under the Constitution, but that the system the administration put in place to classify them as ''enemy combatants'' and review those decisions is inadequate.

The administration had argued that the detainees have no rights, and that the classification and review process was a sufficient substitute for the civilian court hearings that the detainees seek.

President Bush, in Rome for a meeting with Italian Prime Minister Silvio Berlusconi, said the U.S. government will `` abide by the court's decision. That doesn't mean I have to agree with it . . . It's a deeply divided court and I strongly agree with those who dissented. We'll study this opinion.''

In dissent, Chief Justice John Roberts criticized his colleagues for striking down what he called ``the most generous set of procedural protections ever afforded aliens detained by this country as enemy combatants.''

Justices Samuel Alito, Antonin Scalia and Clarence Thomas also dissented.

Scalia wrote that the nation is ''at war with radical Islamists'' and that the court's decision ``will make the war harder on us. It will almost certainly cause more Americans to be killed.''

Justices Stephen Breyer, Ruth Bader Ginsburg, David Souter and John Paul Stevens joined Kennedy in the majority.

In New York, a civil liberties group, which had filed hundreds of unlawful detention petitions for Guantánamo detainees, welcomed the decision.

''The Supreme Court has finally brought an end to one of our nation's most egregious injustices,'' said Vincent Warren, executive director of the Center for Constitutional Rights.

Warren called the Bush administration's decision to strip the detainees of habeas corpus rights a ''six-year-long nightmare'' and ``a lesson in how fragile our constitutional protections are in the hands of an overzealous executive.''

The Supreme Court's ruling came in the case named for Lakhdar Boumediene, a 42-year-old former relief worker who was taken captive by U.S. forces in Sarajevo in 2002. His lawyers said the man -- who has never been charged by the United States with a crime -- had worked for the Islamic counterpart of the Red Cross, the Red Crescent.

His lawyers said that U.S forces spirited Boumediene and five other men from Europe to Turkey to Guantánamo for interrogation after Bosnian police cleared them of plotting to blow up the U.S. Embassy in Sarajevo.