Jailed by the U.S. military and classified by President Bush as an "enemy combatant," the alleged al-Qaida member suspected of plotting to explode a radioactive "dirty bomb" inside the United States could be a serious candidate to face the first military tribunal since last fall's terror attacks, legal analysts said.

But bringing American-born Abdullah al Muhajir, also known as Jose Padilla, before a wartime tribunal would require a significant reversal for the Bush administration. When the president authorized tribunals for suspected terrorists last fall, he excluded U.S. citizens from facing the largely secret military courts.

"There would be nothing to prevent the president from drafting another executive order," said I. Michael Greenberger, who headed counterterrorism efforts at the Justice Department under President Bill Clinton. Still, Greenberger and other lawyers who have studied the potential use of tribunals said, the administration would be better served by pursuing conspiracy charges against Muhajir in civilian court.

"My view is, wiser heads will prevail and this person will be tried in regular federal courts," said Greenberger, now a law professor at the University of Maryland.

Said Jonathan Turley, a law professor at George Washington University: "Here you would have the worst case for the administration - an American citizen who was arrested on American soil who is going to be moved, presumably, outside the American legal system."

That would seem to confer greater rights on a noncitizen, Zacarias Moussaoui, a French citizen of Moroccan descent who is the only person directly charged in the attacks of Sept. 11. He faces trial in federal court in Virginia.

U.S. officials indicated yesterday that, for now, there are no plans to subject Muhajir to a military tribunal, in which the New York native could be tried under looser evidence standards than in a civilian court and have only a limited right to appeal.

Instead, officials said, he was transferred from the custody of the Justice Department to the Defense Department as a way for the government to hold him indefinitely while investigating the alleged bomb plot.

"Our principal interest is in preventing future terrorist attacks," FBI Director Robert S. Mueller III told reporters. "This instance is an example of prevention."

In announcing Muhajir's detention in a television address from Moscow, Attorney General John Ashcroft said U.S. officials had "acted with legal authority both under the laws of war and clear Supreme Court precedent, which establishes that the military may detain a United States citizen who has joined the enemy and has entered our country to carry out hostile acts."

In two prominent cases since the terrorist attacks and subsequent military strikes, government lawyers have faced the question of how to handle U.S. citizens who allegedly fought against their country.

In the most widely known case, American John Walker Lindh, who was born in Maryland and raised in California, faces charges in U.S. District Court in Virginia in connection with his role in a prison uprising last November in northern Afghanistan.

Another U.S. citizen, Yasser Esam Hamdi, who was born in Louisiana to Saudi parents and captured by Northern Alliance soldiers in Afghanistan last fall, has been held for the past two months in Navy custody in Norfolk, Va. No charges have been brought against him, but he has been described as a "battlefield detainee" and has not been permitted to meet with his lawyer.

It would be difficult to classify Muhajir in the same way, said Eugene R. Fidell, president of the National Institute of Military Justice. Instead of being captured in battle, Muhajir was arrested by federal agents May 8 after a flight from Pakistan to O'Hare International Airport in Chicago.

Also, Muhajir was held for more than a month by the Justice Department before President Bush's order late Sunday that transferred the suspected al-Qaida operative to the custody of the U.S. military.

To justify Muhajir's detention, government lawyers cited yesterday a 1942 Supreme Court ruling in the case of eight German agents who slipped into the United States at the start of World War II with plans to destroy factories, bridges and canals.

The men were captured and tried by a secret military tribunal, similar to what President Bush proposed at the outset of the war on terrorism. The high court upheld the use of the tribunal, even for Herbert Hans Haupt, the one German agent who also was a U.S. citizen, and who was executed for his role in the plot.

"Citizenship in the United States ... does not relieve him from the consequences of a belligerency which is unlawful because [it is] in violation of the law of war," the Supreme Court said in the 1942 ruling. "Citizens who associate themselves with the military arm of the enemy government and with its aid, guidance and direction enter this country bent on hostile acts, are enemy belligerents within the meaning of the Hague Convention and the law of war."

Scott L. Silliman, director of the Center for Law, Ethics and National Security at Duke University, said the key question yesterday was why Muhajir was being held under military control. Silliman said the 1942 ruling is not a clear fit with the details of Muhajir's detention, and he said the military's contention that it may indefinitely detain a U.S. citizen faces a strong court challenge from Muhajir's lawyers.

"I think the government is in a quandary," Silliman said. "I think they thought they could move by military commission and they're finding out they can't."