WASHINGTON - The Supreme Court ruled Monday that the war on terrorism does not give the government a "blank check" to hold a U.S. citizen and foreign-born terror suspects in legal limbo, a forceful denunciation of Bush administration tactics since the Sept. 11 attacks.

Ruling in two cases, the high court refused to endorse a central claim of the White House: that the government has authority to seize and detain terrorism suspects and indefinitely deny access to courts or lawyers while interrogating them.

A state of war "is not a blank check for the president when it comes to the rights of the nation's citizens," Justice Sandra Day O'Connor wrote in the most significant case of the day, a ruling that gives American-born detainee Yaser Esam Hamdi the right to fight his detention in a federal court.

Separately, the court said that nearly 600 men from 42 countries held at a Navy prison camp at Guantanamo Bay, Cuba, can use American courts to contest their treatment. The Bush administration had argued that U.S. courts had no business second-guessing detentions of foreigners held on foreign soil.

The administration's detention policies have rankled allies overseas and outraged civil liberties and human rights groups at home.

Deborah Pearlstein, director of the U.S. Law and Security Program at Human Rights First, called Monday's rulings a broad repudiation of the administration's approach.

"The court said any citizen has a right to due process and that the administration's position that it has inherent executive authority ... to detain people is just wrong under the law."

The court declined to rule on the merits of a third case arising from the hunt for terrorists. The justices sent back to a lower court the case of Jose Padilla, a former Chicago gang member and a convert to Islam who is being held as an enemy combatant amid allegations he sought to detonate a radiological "dirty bomb" and blow up apartment buildings in the United States.

The administration contends that all the men at issue in Monday's cases are enemy combatants — neither prisoners of war protected by the Geneva Conventions nor ordinary criminal suspects with automatic rights to see lawyers and know the charges against them.

All the cases dealt with rights of prisoners, an issue with added resonance since recent revelations that U.S. soldiers abused Iraqi prisoners and used harsh interrogation methods at a prison outside Baghdad.

At oral arguments in the terrorism cases in April, an administration lawyer assured the court that Americans abide by international treaties against torture, and that the president or the military would not allow even mild torture as a means to get information.

The Hamdi ruling is the most significant test so far of executive power in the fight to root out and contain global terrorism. The case included multiple holdings and some unusual alliances among conservative and liberal justices.

Eight justices rejected the administration's treatment of Hamdi on some grounds. Only Justice Clarence Thomas , by many measures the court's staunchest conservative, found no fault with the government.

By a vote of 6-to-3, the court placed Hamdi's case back in the hands of a federal judge, who presumably can rule on whether he should be released.

Conservative Justice Antonin Scalia and liberal Justice John Paul Stevens said if the government had a case against Hamdi it should have charged him as a criminal, perhaps even as a traitor. Citizens cannot be held as enemy combatants so long as the usual protections of the Constitution are in force, the pair wrote.

In one bright spot for the government, a majority of five justices rejected that view and held that the president had authority to hold Hamdi as an enemy combatant.

Highlighting that holding, Justice Department spokesman Mark Corallo said, "The military detains enemy combatants to prevent them from continuing to wage terror and war, as well as to gather intelligence to thwart further terrorist assaults."

"Without the ability to detain these dangerous individuals, the American people and our soldiers in combat would face even greater danger from our terrorist enemies."

O'Connor's majority ruling often takes a deferential tone toward the government, but still makes clear that Hamdi's treatment crossed the line.

"Striking the proper constitutional balance here is of great importance to the nation during this period of ongoing combat," O'Connor wrote. "But it is equally vital that our calculus not give short shrift to the values that this country holds dear or to the privilege that is American citizenship."

Hamdi was born in Louisiana in 1980, while his Saudi father worked in the oil industry there. He grew up in Saudi Arabia. Hamdi's family says he was an innocent caught in the wrong place at the wrong time — a 20- year-old relief worker swept up in the chaos of Afghanistan in the weeks following the terrorist attack.

The Bush administration says he was fighting with a Taliban unit and carrying a gun.

After U.S. forces routed the Taliban government, which the United States accused of harboring al-Qaida terrorists responsible for the Sept. 11 attacks, Hamdi was shipped to Guantanamo with other so-called battlefield detainees.

He was eventually transferred to a Navy brig in South Carolina after authorities verified his citizenship.

Padilla, also being held at the brig, was arrested at Chicago's O'Hare airport as he got off a flight from Pakistan more than two years ago, alleged to have plans to mount terror attacks in America.

Both men have been interrogated repeatedly, and until recently were not allowed to meet with lawyers.

The Bush administration had won its arguments in lower court in the Hamdi case but lost in Padilla.

In the Padilla case Monday, a 5-4 majority led by Chief Justice William H. Rehnquist voted to throw out the lower court ruling on a technicality. The court's more liberal wing dissented.

Padilla can refile his case and challenge the government on stronger legal footing, although several lawyers said the government may now choose to file criminal charges instead.

The Supreme Court left for another day many hard questions about what rights enemy combatants may be due, and O'Connor noted that the term remains inexact.

The cases are Hamdi v. Rumsfeld, 03-6696; Rasul v. Bush, 03-334 and Rumsfeld v. Padilla, 03-1027.

The US Supreme Court on Monday sharply restricted the power of the Bush administration to detain terrorism suspects, ruling that foreigners imprisoned at Guantanamo Bay and Americans held as enemy combatants on US soil have the right to challenge their detention in court.

In three separate rulings on detainees, the Supreme Court made no decision on the merits of any of the cases, nor did it order the release of any prisoners. But it clearly rejected the Bush administration's claim that it can detain citizens and non-citizens on the authority of the president alone beyond the reach of any court or law.

The administration has asserted that authority, claiming that those captured in the war on terrorism are unlawful enemy combatants who have neither prisoner-of-war status under the Geneva Conventions nor the right to petition US courts for their release.

The Supreme Court's decision may open a new front in the controversy over US treatment of detainees in Guantanamo. It was unclear whether the ruling could apply elsewhere. Legal experts said the court ruling indicated that detainees may have the right to bring lawsuits against the US government under a statute known as the Alien Tort Claims Act if they believe they have been wrongfully imprisoned, abused or tortured.

"The lesson of this decision is that there is no prison beyond the reach of domestic law," said Joseph Margulies, who represented Australian detainee David Hicks.

Lawyers for the detainees said they would move immediately to file petitions with US courts seeking access to the prisoners and reports on their conditions, and would seek a review on whether they were being held lawfully.

Clive Stafford-Smith, a UK lawyer who also acted for four of the UK detainees, called the verdict "a stinging rebuke for the lawless policies of the Bush administration", and said cases would be filed on behalf of UK detainees.

In the Guantanamo decision, which involved foreign prisoners at a US military base in Cuba, the court ruled 6-3 that US federal courts have jurisdiction to consider the claims of terrorism suspects held there.

The justices set no limits on what issues could be challenged by the detainees in court. But they also stressed that the courts themselves would decide what standard of evidence would be required to defend the detentions, and that some courts might accept the outcome of a military review that concludes the detention is legitimate.

The Guantanamo ruling was tempered by the judgment in a related case involving an American held as an enemy combatant on US soil. The court ruled by a different 6-3 majority that Yaser Esam Hamdi also had the right to challenge his detention. "A state of war is not a blank cheque for the president when it comes to the rights of the nation's citizens," Justice Sandra Day O'Connor (news - web sites) wrote for the majority.

But in an effort to reconcile Mr Hamdi's rights with US security needs, the majority found that the government need only provide the courts with "credible evidence", including hearsay, that Mr Hamdi had been properly determined to be an enemy combatant.

That finding may allow the US to defend successfully before the courts its decision to hold many of the detainees in Guantanamo and elsewhere.