The future of Guantanamo Bay is unclear as the debate over fighting terrorism centers on whether it is a war or a criminal action.

By JONATHAN MAHLER

WASHINGTON - A military charter plane left Guantanamo Bay, Cuba, on November 25 for Sana, Yemen, carrying Osama bin Laden’s former driver, Salim Hamdan. Once the Bush administration’s example for the war on terror, Mr.Hamdan will spend less than a month in a Yemeni prison before returning to his family in Sana, having been acquitted by a jury of United States military officers of the most serious charge brought against him, conspiracy to support terrorism.

The turn of events underscores the central challenge President Obama will face as he defines his approach to fighting terrorism - and the imperative for him to adopt a new, hybrid plan, one that blends elements of both traditional military conflict and criminal justice.

Much of the debate over how to battle terrorism has centered on two conflicting paradigms: Is it a war or a criminal action- The Hamdan case highlights the limitations of such binary thinking. As the verdict made clear, he was not a criminal conspirator in the classic sense. Yet, as an aide to the world’s most dangerous terrorist, neither was he a conventional prisoner of war .

So how should Americans think about Mr.Hamdan? How should they think about the fight against terrorism?

The problems with the war paradigm are by now familiar. Because the war on terror is unlike any other the United States has waged, traditional wartime policies and mechanisms have made for an awkward fit, in some instances undermining efforts to defeat terrorism. The traditional approach to captured combatants - holding them until the end of hostilities - is untenable in a war that could last for generations.

If you treat the fight against terrorism as a war, it’s hard to get around the argument that it’s a war without boundaries; a terrorist could be hiding anywhere. Yet by asserting the right to round up suspected terrorists in other sovereign nations and indefinitely detain and interrogate them without hearings or trials, the administration complicated its efforts to build an international coalition against terrorism.

“The war-against-Al-Qaeda paradigm put us in a position where our legal authorities to detain and interrogate didn’t match up with those of our allies, so we ended up building a system that’s often rejected as strategically unsound and legally suspect by even our closest allies,” says Matthew Waxman, a law professor at Columbia University in New York who worked on detainee issues in the Bush administration.

Perhaps the most problematic consequence of the war paradigm, though, is that it gave the president enormous powers - as commander in chief - to determine how to detain and interrogate captured combatants.

Some are now urging President-elect Obama to abandon the war paradigm in favor of a pure criminal-justice approach, which is to say, either subject captured combatants to criminal trials or let them go. This will almost certainly not happen. Ceding the military paradigm altogether would severely limit Mr.Obama’s ability to fight terrorism.

The fight against terrorism will have to be something of a hybrid. This is a novel idea, as the United States Constitution lays out only two distinct options: the country is at war, or it is not.

There has been talk of creating a national security court within the federal judiciary that would presumably give more flexibility on matters like, say, the standard of proof for evidence collected on an Afghan battlefield. Similarly, it may be necessary to set clear legal guidelines for when the government can detain enemy combatants, and how far C.I.A. agents can go when interrogating terror suspects.

Such an approach might enhance a president’s power.“We need a strong president to fight this war,” says Jack Goldsmith, a law professor at Harvard who worked in the Bush Justice Department, “and the way to ensure that there’s a strong president is to have the other institutions on board for the actions he feels he needs to take.”

Jonathan Mahler, a contributing writer for The Times Magazine, is the author,most recently, of “The Challenge: Hamdan v. Rumsfeld and the Fight Over Presidential Power.”