ASHINGTON, Feb. 20 — The Supreme Court agreed on Friday to consider whether President Bush had the authority to detain indefinitely an American who was seized on American soil by declaring him an enemy combatant.

The justices said they would agree to the request to review a ruling in December by a federal appeals court in New York that Mr. Bush had overstepped his constitutional bounds in detaining the man, Jose Padilla, and denying him access to a court or any review outside the executive branch.

In agreeing, with a one-page order, to review the case, the Supreme Court all but assured that Mr. Padilla's case would be argued in April along with two other cases that go to the heart of the administration's assertion of sweeping powers after the Sept. 11, 2001, attacks and the Afghan conflict.

That means that the most serious questions in the roiling debate over balancing civil liberties concerns and national security needs will converge before the Supreme Court in the last week of April. By agreeing to hear all three cases, the justices have squarely taken on the obligation to provide the final legal word in rulings that will probably be handed down in late spring.

The justices had already agreed to hear in April an appeal of whether the president may similarly detain indefinitely as an enemy combatant another American, who was captured not on American soil but, the authorities say, on the battlefield in Afghanistan. A federal appeals court in Richmond, Va., has ruled that as a wartime president, Mr. Bush has the authority to detain that man, Yaser Esam Hamdi. Mr. Hamdi, a citizen because he was born in Baton Rouge, La., of Saudi parents, is in the same naval brig in Charleston, S.C., as Mr. Padilla.

The administration has said Mr. Padilla, who was arrested in 2002 at O'Hare International Airport in Chicago, is a former gang member from Chicago who plotted with operatives of Al Qaeda overseas to detonate a "dirty" radiological bomb in the United States.

In addition, the court will hear oral arguments on whether the military control of 650 detainees at the naval base at Guantánamo Bay, Cuba, puts them beyond the reach of American law. Two federal appeals courts, the level just below the Supreme Court, have reached opposite conclusions on that question. The administration has argued that the base, on the southeastern tip of Cuba, is outside the sovereign territory of the United States and thus beyond the reach of the Constitution, a position that the United States Court of Appeals for the District of Columbia Circuit accepted.

A panel of the United States Court of Appeals for the Ninth Circuit, in San Francisco, held in a divided ruling that the base is under the undisputed control of the United States and that the detainees have a right to file for relief in federal court.

The three cases and their resolution are widely viewed by legal experts as having profound and long-lasting implications for how power is apportioned between the executive and judicial branches, especially in a time of war.

"The Supreme Court's decision to hear the Padilla case sends a strong message that the power of the president to detain American citizens is subject to limits in the Constitution and review in the courts," said Deborah Pearlstein, who directs the U.S. Law and Security Program at Human Rights First, the former Lawyers Committee for Human Rights, in Manhattan. "Together with appeals the court will hear in several related cases, this case has the potential to change the landscape of American law."

Attorney General John Ashcroft said it was critical that the court affirm Mr. Bush's authority to detain people he deems enemy combatants.

"The president," Mr. Ashcroft said, "acting as commander in chief in a time of war, determined that Padilla is closely associated with Al Qaeda, an international terrorist organization with which the United States is at war; that he has engaged in conduct that constituted hostile and warlike acts; that he possesses intelligence that would aid U.S. efforts to prevent attacks by Al Qaeda; that he represents a grave danger to the national security; and that it is in the interest of the United States to detain Padilla as an enemy combatant."

Although the administration has argued that the government is not obliged to let Mr. Hamdi or Mr. Padilla meet lawyers, they have been permitted to do so in recent weeks. Officials said they had determined that letting the detainees meet lawyers would no longer impede questioning, as they contended it would have done earlier.

In its decision last year involving Mr. Hamdi, the United States Court of Appeals for the Fourth Circuit, in Richmond, said the president was due extraordinary deference in a time of war.

In ruling in Mr. Padilla's favor, the two judges in the majority of a panel of the United States Court of Appeals for the Second Circuit, in Manhattan, said, "The president, acting alone, possesses no inherent constitutional authority to detain American citizens seized within the United States, away from the zone of combat, as enemy combatants."