The judges on Monday said they lacked jurisdiction under the strict definition of those eligible for trial by military tribunal under a law enacted last year.

The Defense Department "will make a determination as to whether it's appropriate to file an appeal or not," Fratto said. "It does show that the system is taking great care to be within the letter of the law."

Defense Secretary Robert Gates, who was traveling in Asia, said he was not familiar with the details of the ruling.

"If it is as described, that's the reason we have a judicial process in all of this and we'll have to take a look at it and see what the implications are," he said.

Setback for administration
The rulings did not affect U.S. authority to indefinitely hold the terrorism suspects detained at the Guantanamo Bay naval base in southeast Cuba.

But it was the latest setback for the Bush administration's efforts to put the Guantanamo captives through some form of judicial process.

"In no way does this decision affect the appropriateness of the military commission system," Fratto said.

The surprise decisions do not spell freedom for the detainees.

Salim Ahmed Hamdan of Yemen and Omar Khadr, a Canadian who was 15 when he was arrested on an Afghan battlefield, were the only two of the roughly 380 prisoners at Guantanamo charged with crimes under a reconstituted military trial system.

Experts blame haste

Defense attorneys and legal experts blamed the rush by Congress and President Bush last year to restore the war-crimes trials after the U.S. Supreme Court threw out the previous system, declaring it unconstitutional. In a remarkable coincidence, it was Hamdan's lawsuit that wound up in the Supreme Court.

In both of Monday's cases, the judges ruled that the new legislation says only "unlawful enemy combatants" can be tried by the military trials, known as commissions. But Khadr and Hamdan previously had been identified by military panels here only as enemy combatants, lacking the critical "unlawful" designation.

"The fundamental problem is that the law was not carefully written," said Madeline Morris, a Duke University law professor. "It was rushed through in a flurry of political pressure from the White House ... and it is quite riddled with internal contradictions and anomalies."

Prosecuting attorneys in both cases indicated they would appeal the dismissals. But the court designated to hear the appeals - known as the court of military commissions review - doesn't even exist yet, said Marine Col. Dwight Sullivan, chief of military defense attorneys at Guantanamo Bay.

Army Maj. Beth Kubala, spokeswoman for the Office of Military Commissions that organizes the trials, said "the public should make no assumption about the future of military commissions."

She said they will continue to operate openly and fairly and added that dismissals of the charges "reflect that the military judges operate independently."

She declined to comment on how the Office of Military Commissions planned to respond to the setbacks, saying she didn't want to speculate.

Military prosecutors declined to appear before reporters after their cases collapsed.

The distinction between classifications of enemy combatants is important because if they were "lawful," they would be entitled to prisoner of war status under the Geneva Conventions.

A Pentagon spokesman said the issue was little more than semantics.

Navy Cmdr. Jeffrey Gordon said the entire Guantanamo system deals with people who act as "unlawful enemy combatants," operating outside any internationally recognized military, without uniforms or other things that make them party to the Geneva Conventions.

"It is our belief that the concept was implicit that all the Guantanamo detainees who were designated as 'enemy combatants' ... were in fact unlawful," Gordon said.

But Morris said the Military Commissions Act defines a lawful enemy combatant, in addition to a uniformed fighter belonging to a regular force - as "a member of a militia, volunteer corps or organized resistance movement belonging to a state party engaged in such hostilities and who meets four additional criteria."