In Hamdi v. Rumsfeld, five justices of the Supreme Court said in 2004 that Congress had granted the president power to detain at least those enemy combatants captured on the battlefield in Afghanistan, even if they were American citizens, for the duration of hostilities there. But the detainee in that case, Yaser Hamdi, was freed and sent to Saudi Arabia not long after the court’s decision, which also allowed him to challenge his detention.

Based on the Hamdi decision, the Fourth Circuit in 2005 upheld the detention of Jose Padilla, an American arrested at a Chicago airport. Although Mr. Padilla was said to have ties to Al Qaeda, the Fourth Circuit decision largely turned on his activities on the battlefield in Afghanistan. Just before the Supreme Court was to decide whether to hear his case for a second time, Mr. Padilla was transferred to the criminal justice system. He was convicted last year on charges related to terrorism.

The Supreme Court’s decision in Mr. Marri’s case may be quite limited, given his unique status, or quite broad.

The divided three-judge Fourth Circuit panel that ruled in June 2007 for Mr. Marri, in a decision later vacated by the full court, based its ruling on a proposition that could be applied broadly should the Supreme Court adopt it. Judge Diana Gribbon Motz wrote for the majority that Mr. Marri was a civilian and may not be detained by the military.

Because Mr. Marri was not alleged to have fought with the Taliban or the armed forces of any enemy nation or to have engaged in combat with United States forces, Judge Motz reasoned, President Bush was powerless to have the military detain him, just as he could not have ordered the military detentions of “the Unabomber or the perpetrators of the Oklahoma City bombing.”

In a recent brief, the government provided the justices with a sworn 2004 statement from Jeffrey N. Rapp, the military intelligence official. The statement, declassified in 2006, said Mr. Marri had met with Osama bin Laden and Khalid Sheikh Mohammed, the chief 9/11 plotter, in the summer of 2001. “Al-Marri offered to be an Al Qaeda martyr or to do anything else that Al Qaeda requested,” Mr. Rapp said. The Qaeda leaders told Mr. Marri, the statement said, to leave for the United States and to make sure he got there before Sept. 11.

The government’s brief said Congress must have intended to allow the detention of people like Mr. Marri and called a contrary interpretation absurd. Such a reading, the brief said, “relies on the assumption that when Congress authorized the use of military force to respond to the Sept. 11 attacks, it did not intend to reach individuals virtually identically situated to the Sept. 11 hijackers.”