The president lacks the authority to indefinitely hold without charges Al Qaeda operatives who are caught in America, a federal appellate court ruled yesterday.

The 2–1 ruling rejected President Bush’s theory of the expansive powers of his office and distinguished between the rights afforded to terror suspects arrested domestically and those captured abroad. The U.S. 4th Circuit Court of Appeals, which sits in Richmond, Va., ordered the government to either deport, detain as a witness, or criminally charge a Qatar national, Ali al-Marri, who the government claims is a Qaeda sleeper agent sent to this country on September 10, 2001, for a second round of terror strikes.

Mr. Marri is the only individual known to have been arrested in this country who remains classified as an “enemy combatant.” Previously, a federal judge invited him to present evidence challenging his combatant designation, but his lawyers refused, arguing that the very designation as an “enemy combatant” was illegal. The 4th Circuit sided with Mr. Marri yesterday, writing that “in this nation, military control cannot subsume the constitutional rights of civilians.”

In asserting a legal authority to hold Mr. Marri, President Bush was “making a claim to power that would so alter the constitutional foundations of our Republic,” the majority wrote.

“For a court to uphold a claim to such extraordinary power,” the court wrote, “would effectively undermine all of the freedoms guaranteed by the Constitution.”

At the center of the court’s reasoning is the fact that Mr. Marri was lawfully in this country at the time of his arrest. That fact, the court found, guaranteed Mr. Marri the same legal protections as any other accused criminal, including domestic terrorists such as the Unabomber or the perpetrators of the Oklahoma City bombing.

“Put simply, the Constitution does not allow the President to order the military to seize civilians residing within the United States and detain them indefinitely without criminal process, and this is so even if he calls them ‘enemy combatants,'” the majority found.

Judge Diana Motz wrote the decision, which was joined by Judge Roger Gregory. The majority decision stresses that Mr. Marri was lawfully in this country, and it leaves open the question as to whether Mr. Bush could detain on military authority a person here illegally.

In a dissent, Judge Henry Hudson wrote that Mr. Marri could be considered an “enemy combatant” even if he was not found armed and did not serve a state at war with America.

“Although al-Marri was not personally engaged in armed conflict with U.S. forces, he is the type of stealth warrior used by Al Qaeda to perpetrate terrorist acts against the United States,” Judge Hudson wrote.

At the time of his arrest in 2001, Mr. Marri was living in Peoria, Ill. He was originally charged with giving false statements and credit card fraud, but in 2003, the government dismissed the charges and classified him as an enemy combatant. His lawyers say he is currently in a naval brig in Charleston, S.C.

In response to the ruling, the Justice Department released a statement that said: “The President has made clear that he intends to use all available tools at his disposal to protect Americans from further Al Qaeda attack, including the capture and detention of Al Qaeda agents who enter our borders.”

The statement reiterated allegations that Mr. Marri trained at a terrorist camp in Afghanistan and had met with the man reported to have masterminded the September 11, 2001, terrorist attacks — Khalid Sheikh Mohammed.

“In the United States, we don’t jail people for life on the hearsay statements of faceless government bureaucrats,” a lawyer for Mr. Marri, Jonathan Hafetz of the Brennan Center for Justice at New York University, said. “If the government claims he’s a bad person, the way we do it in the United States is we charge that person with a crime and give that person an opportunity to demonstrate his innocence at trial.”

One law professor at George Mason University, Michael Krauss, said the decision cut into the president’s power to wage war.

The decision, Mr. Krauss said, grants legal immigrants “the right to due process of American civilian courts even if you wage war against the USA from inside the borders.”