In two crucial decisions today on the scope of presidential wartime powers, the Supreme Court rejected the Bush administration's claim that it can hold suspected terrorists or "enemy combatants" on American soil without giving them a day in court.

The court said detainees, whether American citizens or not, retain their rights, at least to a legal hearing, even if they are held at the U.S. naval base in Guantanamo Bay, Cuba. Guantanamo Bay is under U.S. control and thus appropriately within the jurisdiction of U.S. courts, the high court ruled.

The president's constitutional powers, even when supported by Congress in wartime, do not include the authority to close the doors to an independent review of the legality of locking people up, the justices said.

"We have long since made clear that 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 Hamdi et al v. Rumsfeld.

The rulings were the court's most significant statement in decades on the scope of presidential war powers to deal with "enemy combatants," such as someone seized on a battlefield in Afghanistan. Those powers, under the constitution, are insufficient to close the doors of the federal courts, the high court said.

The administration's detention policies have been among the most controversial outgrowths of its war on terrorism, provoking significant political and legal debate between those who felt the government had gone too far and those who believed its actions were intrinsic to the president's constitutional role as commander-in-chief.

Four justices -- a plurality -- said congress did indeed authorize detention of citizens. But the administration secured only one vote -- that of Justice Clarence Thomas -- for the proposition of detention of a citizen without any hearing. Thomas, dissenting, said he would affirm the lower court ruling overturned today.

The decisions came in a package of cases all related to arrests after Sept. 11, 2001, of people deemed terrorists or enemy combatants by the government.

The cases were Hamdi et al v. Rumsfeld and Rasul et al v. Bush. In a third related case, the court declined on technical grounds to rule on the merits of a challenge brought by Jose Padilla, who was arrested in Chicago after a flight from Pakistan, sending the case back to a lower court in South Carolina.

O'Connor was joined in the Hamdi case by Chief Justice William H. Rehnquist and Justices Anthony M. Kennedy and Stephen G. Breyer. Justices David H. Souter and Ruth Bader Ginsburg agreed with O'Connor's result, but took issue with the plurality's holding that the detentions were implicitly sanctioned by Congress when it voted to authorize the use of force in the war on terrorism.

Justices Antonin Scalia and John Paul Stevens dissented but not in support of the administration. Indeed, Scalia declared that there is only one way to prosecute citizens accused of aiding the enemy -- to treat them as "traitors subject to the criminal process."

". . . A view of the Constitution that gives the Executive authority to use military force rather than the force of law against citizens on American soil flies in the face" of the Constitution and of American traditions, Scalia wrote.

In the Rasul case, which involved foreigners held at Guantanamo, Stevens wrote for the court, joined by O'Connor, Souter, Ginsburg and Breyer. Scalia, Rehnquist and Thomas dissented, saying that foreigners arrested overseas do not have access to the U.S. courts.

"Today's historic rulings are a strong repudiation of the administration's argument that its actions in the war on terrorism are beyond the rule of law and unreviewable by American courts," Steven Shapiro of the American Civil Liberties Union said in a statement.

Michael Ratner of the Center for Constitutional Rights, which brought the Guantanamo case, said, "This is a major victory for the rule of law and affirms the right of every person, citizen or noncitizen, detained by the United States to test the legality of his or her detention in a U.S. court."

The administration was "reviewing the Court's decision to determine how to modify existing processes to satisfy the Court's rulings," a Justice Department spokesman said in a statement.

The spokesman, Mark Corallo, also said the administration was pleased the court "upheld the authority of the President as Commander-in-Chief of the armed forces to detain enemy combatants, including U.S. citizens. This authority is crucial in times of war whether the enemy combatants are individuals who join our enemies on the battlefield to fight against America and its allies, or whether they are individuals who infiltrate our border to commit hostile and war-like acts against our nation."

Yaser Esam Hamdi, an American citizen born in Louisiana, was captured by the Northern Alliance in Afghanistan in 2001 and turned over to the U.S. military, which transferred him to a brig in Charleston, S.C. Hamdi's father sought a habeas corpus review of his son's imprisonment. The government, supported by the U.S. Court of Appeals for the Fourth Circuit, contended that as an enemy combatant, he could be held indefinitely without formal charges or proceedings.

O'Connor wrote that the congressional resolution authorizing the use of force against terrorism did indeed support detention of Hamdi. But neither that act nor the constitution overrides "the fundamental nature of a citizen's right to be free from involuntary confinement by his own government without due process of law . . . "

"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."

She said a citizen detained in this fashion must receive notice of the "factual basis" for his classification and be given a "fair opportunity" to rebut the claim before "a neutral decisionmaker."

The opportunity for rebuttal need not be a conventional federal court hearing, with all its strict rules of evidence and process, she added.

But "due process demands some system for a citizen detainee to refute his classification," she said. While an "appropriately authorized and properly constituted military tribunal" might suffice, even then "a court that receives a petition for a writ of habeas corpus from an alleged enemy combatant must itself ensure that the minimum requirements of due process are achieved."

The second of today's decisions involved non-citizens, specifically, two Australians and twelve Kuwaitis, who were captured abroad during hostilities between the U.S. and the Taliban in Afghanistan.

The government relied on a World War II era case called Eisentrager, in which the Supreme Court denied a habeas corpus hearing to German citizens captured in China, convicted of war crimes by a military commission and imprisoned in occupied Germany.

Stevens said that case did not apply. The enemy combatants in today's case, he said, are not nationals of countries at war with the U.S.

Unlike the Germans, they have never been afforded access to any tribunal, "much less charged with and convicted of wrongdoing," Stevens wrote.

"And for more than two years they have been imprisoned in territory [Guantanamo] over which the United States exercises exclusive jurisdiction and control," he continued.

Moreover, Stevens wrote, nothing in the law or in previous rulings "excludes aliens detained in military custody outside the United States" from seeking hearings in the federal courts.

Scalia, in dissent, wrote that the "consequence of this holding, as applied to aliens outside the country, is breathtaking. It permits an alien captured in a foreign theater of active combat to bring" suit against the Secretary of Defense.

"The Commander in Chief and his subordinates had every reason to expect that the internment of combatants at Guantanamo Bay would not have the consequence of bringing the cumbersome machinery of our domestic courts into military affairs," Scalia wrote.