ASHINGTON, Jan. 8 — A federal appeals court handed the Bush administration a major legal victory today in ruling that a wartime president can indefinitely detain a United States citizen captured as an enemy combatant on the battlefield and deny that person access to a lawyer.
The case, which set up a stark clash between the nation's security interests and its citizens' civil liberties, may have expanded the power of the presidency as the three-judge panel ruled unanimously that President Bush was due great deference in conducting the war against terrorism.
The judges of the United States Court of Appeals for the Fourth Circuit, in Richmond, Va., said it was improper for the federal courts to probe too deeply into the detention of Yasser Esam Hamdi, a 22-year-old American-born Saudi who was captured on the battlefield in Afghanistan and is now imprisoned in a military brig in Norfolk, Va.
Lawyers for Mr. Hamdi challenged his detention, asserting that because he is a citizen he has the same constitutional rights as citizens in criminal cases, including the right to consult a lawyer and to question the reasons for his confinement.
The appeals panel said that to deprive any citizen of his constitutional protections "is not a step that any court would casually take."
Even so, in the opinion written by the circuit's chief judge, J. Harvie Wilkinson III, the panel said, "The safeguards that all Americans have come to expect in criminal prosecutions do not translate neatly to the arena of armed conflict. In fact if deference is not exercised with respect to military judgments in the field, it is difficult to see where deference would ever obtain."
Attorney General John Ashcroft called the decision "an important victory for the president's ability to protect the American people in times of war."
But Elisa Massimino, a director of the Lawyers Committee for Human Rights, said: "The court seems to be saying that it has no role whatsoever in overseeing the administration's conduct of the war on terrorism. That is particularly disturbing in the context of a potentially open-ended, as-yet-undeclared war, the beginning and end of which is left solely to the president's discretion."
The lawyers authorized by Mr. Hamdi's father to argue the case on his son's behalf are certain to seek a review from the Supreme Court, but there is no guarantee that the justices will take up the case.
The only other American citizen known to be held without charges is Jose Padilla, the so-called dirty-bomb suspect. Unlike Hamdi, who was captured on a battlefield in Afghanistan, Mr. Padilla was arrested at O'Hare International Airport in Chicago on suspicion of being involved in a terrorist plot to detonate a radioactive device. He is being held in a military brig in South Carolina.
Today's ruling may be the most far-reaching yet in a host of court cases brought on by the administration's efforts in the war against terrorism.
In one case, a federal district judge has upheld the administration's decision to hold about 600 prisoners at the Guantánamo naval base in Cuba, ruling that the laws of the United States do not apply there.
Other federal judges have ruled that the Bush administration could not hold hearings on immigration violations in secret and could not withhold the names of those arrested on such charges from the public. Those cases are making their way through the appellate courts.
The Hamdi case began with the narrow issue of whether the courts should be satisfied with a Defense Department official's two-page, nine-paragraph statement that offered a spare accounting of facts to justify the government charge that Mr. Hamdi has been properly labeled an enemy combatant.
Judge Robert G. Doumar of Federal District Court in Norfolk ruled in August that the declaration — made by Michael Mobbs, a special adviser to the under secretary of defense for policy — was not enough.
The appeals court reversed that finding today and went much further in defining the authority of the executive branch in wartime.
"The constitutional allocation of war powers affords the president extraordinarily broad authority as commander in chief and compels courts to assume a deferential posture in reviewing exercises of this authority," the panel found.
While courts are entitled to review detentions when asked, the panel ruled that, "courts are ill-positioned to police the military's distinction between those in the arena of combat who should be detained and those who should not."
The panel said it would be improper for the judicial branch to launch an exhaustive inquiry into the conditions of Mr. Hamdi's capture, as his lawyers had requested. To do so, the judges said, would require officers to travel back to the United States from across the globe. They said the conduct of the war should not be determined by litigation.
The appeals court did not go so far as to deny Mr. Hamdi the use of the writ of habeas corpus, a legal mechanism allowing people to challenge their detention, a position that might attract a Supreme Court review. Instead, the judges said the judicial inquiry had to be extremely limited.
Frank W. Dunham Jr., a federal public defender in Virginia who argued the case for Mr. Hamdi, had asserted that the defendant was entitled to challenge the accusations that he was an enemy soldier.
But the court said that since it was "undisputed" that Mr. Hamdi "was present in a zone of active combat operations, we are satisfied that the Constitution does not entitle him to a searching review of the factual determinations underlying his seizure there."
In addition, the judges rejected appeals by Mr. Hamdi's lawyers that they should consider whether the war was at an end. Such questions, the court said, were solely the province of the president and his military advisers.
The judges also rejected Mr. Hamdi's assertion that the Geneva Convention required the government to convene a tribunal to determine if he was a lawful or unlawful combatant. The panel said that only governments and diplomats could invoke the Convention, not individuals.
Judge Wilkinson ended the opinion with a reference to the casualties of the Sept. 11 attacks.
"It is not wrong even in the dry annals of judicial opinion to mourn those who lost their lives that terrible day," he wrote. "Yet we speak in the end not from sorrow or anger, but from the conviction that separation of powers takes on special significance when the nation itself comes under attack."
Judge Wilkinson was joined on the panel by Judge William W. Wilkins and Judge William B. Traxler. Judge Wilkinson and Wilkins were appointed by President Ronald Reagan. Judge Traxler was first named to the bench by the first President Bush and elevated to the appeals court by President Bill Clinton.