The court did not rule on the spying program's legality. Instead, the decision found that the American Civil Liberties Union, academics, lawyers and journalists who brought the case did not have standing to sue because they could not demonstrate that they had been direct targets of the clandestine surveillance.

The decision vacates a ruling in the case last August by a U.S. District Court judge in Detroit, who found that the administration's program to monitor private communications violated the Bill of Rights and a 1970s federal law, the Foreign Intelligence Surveillance Act.

Friday's action in the 6th Circuit means that the principal remaining legal challenge to the NSA's Terrorist Surveillance Program is a group of cases pending before a U.S. District Court judge and the U.S. Court of Appeals for the 9th Circuit in California.

The primary issue before that appeals court, differing somewhat from that in

the Michigan case, is whether the administration may claim that a privilege covering state secrets precludes the litigation.
In January, after Democrats gained control of Congress, the administration abruptly shifted its position. Attorney General Alberto Gonzales announced that the surveillance program would start to be overseen by a court established to hear FISA cases.

But administration officials have not described critical details of the new approach, including whether a separate warrant is required for each instance of monitoring. Aides to Bush also have asserted that the president still retains the authority to conduct surveillance without court permission.

Judge Ronald Lee Gilman, a Democratic appointee, disagreed in a dissenting opinion in which he concluded the plaintiffs were entitled to sue because they felt a need to alter their communications after the program was disclosed. Gilman also wrote that the case was not moot because "the president maintains that he has the authority to 'opt out' of the FISA framework at any time," and he agreed with the lower court judge that the program violates federal law.

Administration officials lauded the 6th Circuit's decision. Deputy White House press secretary Tony Fratto called the lower court finding that the program was unconstitutional "wrongly decided." Fratto said the appellate court "properly determined that the plaintiffs had failed to show their claims were entitled to review in federal court."

The ACLU's legal director, Steven Shapiro, said, "As a result of today's decision, the Bush administration has been left free to violate the Foreign Intelligence Surveillance Act, which Congress adopted almost 30 years ago to prevent the executive branch from engaging in precisely this kind of unchecked surveillance."

Shapiro said the ACLU was examining its legal options, including the possibility of an appeal to the Supreme Court.