Cincinnati ? A divided federal appeals court rejected a lawsuit Friday challenging President Bush’s domestic spying program without ruling on the issue of whether warrantless wiretapping is legal.

In a 2-1 decision with Republican-appointed judges in the majority, a three-judge panel of the 6th U.S. Circuit Court of Appeals said the plaintiffs had no standing to sue because they couldn’t prove their communications had been monitored by the government.

The decision underscored the difficulty of challenging the anti-terrorism program in court because its secret nature prevents plaintiffs from obtaining surveillance information. The National Security Agency had refused to turn over information about the warrantless wiretapping that would have bolstered the court case.

“This is a Catch-22,” said Steven R. Shapiro, legal director of the American Civil Liberties Union, which filed the lawsuit. “I think what in effect they’re saying is that we can’t tell you whether you have been wiretapped because that’s a secret. And unless you know you’ve been wiretapped, you can’t challenge that program.”

The appeals court vacated a 2006 order by a lower court in Detroit, which had concluded that the warrantless surveillance authorized after the Sept. 11, 2001, terrorist attacks was unconstitutional.

President Bush authorized warrantless monitoring of international telephone calls and e-mails to or from the United States when one party is believed to be a terrorist or to have terrorist ties. The government has kept details confidential, saying the case involved state secrets whose disclosure would threaten national security.

While sidestepping the question of constitutionality, Judge Alice M. Batchelder and Judge Julia Smith Gibbons wrote that the plaintiffs lacked standing to sue without proof they were monitored by the government.

“The plaintiffs are ultimately prevented from establishing standing because of the state secrets privilege,” Gibbons wrote.

Judge Ronald Lee Gilman, a Democratic appointee, disagreed, saying the plaintiffs were within their rights to sue and that it was clear the surveillance program violated the Foreign Intelligence Surveillance Act of 1978. The government had said it sometimes needed to act without waiting for the secret Foreign Intelligence Surveillance Court, established by the 1978 law.

Earlier this year, the Bush administration said the eavesdropping program is now overseen by a special federal intelligence court, so the case was moot. But, by sidestepping the constitutionality of the surveillance program, the appeals court left open the possibility that Bush or another president could restart the program, and opponents contend that means the case remains relevant.

The appellate decision didn’t address the legality of the program or absolve the administration of complying with a congressional subpoena seeking information, said Sen. Patrick Leahy, D-Vt., who is head of the Senate Judiciary Committee.

“There is a dark cloud over the White House’s warrantless wiretapping program, and a full response to the outstanding subpoena from the Senate Judiciary Committee by this Administration would be a good start to clearing the air,” Leahy said in a statement.