WASHINGTON, 13 June 2007 — The White House suffered another serious legal blow in its “war on terror” on Monday when a court ruled that the military could not indefinitely detain a Qatari citizen captured in the US. The ruling is a stinging rejection of one of the Bush administration’s central assertions about the scope of executive authority to combat terrorism.

In the ruling, the Federal Court of Appeals in Richmond, Virginia, ordered the Bush administration to transfer Ali Saleh Kahlah Al-Marri — a computer science student arrested in Illinois in connection with the Sept. 11 attacks — to the criminal court system. Al-Marri, currently held in military custody in Charleston, SC, is the only person in the United States known to be held as an enemy combatant.

The court said the administration may charge Al-Marri with a crime, deport him or hold him as a material witness in connection with a grand jury investigation.

“But military detention of Al-Marri must cease,” Judge Diana Gribbon Motz wrote for the majority of a divided three-judge panel.

“The president lacks the power to order the military to seize and indefinitely detain Al-Marri,” wrote Judge Motz in the 2-1 decision. “We have found no authority for holding that the evidence offered by the government affords a basis for treating Al-Marri as an enemy combatant, or as anything other than a civilian.”

The court said a fundamental principle is at stake: Military detention of someone who had lawfully entered the United States and established connections here, it said, violates the constitution.

“To sanction such presidential authority to order the military to seize and indefinitely detain civilians,” Judge Motz wrote, “even if the president calls them ‘enemy combatants,’ would have disastrous consequences for the constitution — and the country.”

“We refuse to recognize a claim to power,” Judge Motz added, “that would so alter the constitutional foundations of our republic.”

The decision is the second setback for the administration in as many weeks. Last week, military judges at Guantanamo Bay ruled Congress had not authorized the administration to try “enemy combatants” at military commissions.

The Justice Department said on Monday it would appeal. In a statement, the Justice Department said it would ask the court to rehear the case, which could eventually reach the Supreme Court. The statement added that Al-Marri represented a danger to the United States.

“If the president had his way, he would have virtually unlimited authority to detain any noncitizen on his say-so, place him in indefinite military custody, and deny him access to court to challenge the detention,” said Jennifer Daskal of Human Rights Watch. “This decision should remind the president that even he is not above the law.”

Al -Marri was arrested in 2001, in Peoria, Ill., where he was charged with credit-card fraud and lying to federal agents. He was on the verge of a trial on those charges when he was moved into military detention in 2003. He has been held for the last four years at the navy brig in Charleston. For his first 16 months in the brig, Marri was allowed no contact with his family or lawyers. He was denied basic necessities and subjected to extreme sensory deprivation, a lawsuit filed on his behalf in 2005 said.

Two other men have been held as enemy combatants on the American mainland since the Sept. 11 attacks. One, Yasser Hamdi, was freed and sent to Saudi Arabia after the Supreme Court allowed him to challenge his detention in 2004. The other, Jose Padilla, was transferred to the criminal justice system last year. He is currently on trial on terrorism charges in federal court in Miami.