The Bush administration asked a federal appeals court Monday to toss out a lawsuit challenging a warrantless surveillance program, saying the government can't defend itself without revealing national secrets.

The American Civil Liberties Union sued the National Security Agency in January on behalf of journalists, scholars and lawyers who say the surveillance has made it difficult for them to do their jobs because they believe many of their overseas contacts are likely targets.

"This suit must be dismissed because its very subject matter is a state secret, and litigation would inevitably result in disclosing state secrets," Justice Department lawyers wrote in a brief filed Monday.

U.S. District Judge Anna Diggs Taylor in Detroit ruled in August that the program violates the rights to free speech and privacy and the separation of powers.

The Justice Department appealed to the 6th U.S. Circuit Court of Appeals in Cincinnati, which ruled that the administration could keep the program in place during the appeal.

The Bush administration secretly launched the surveillance program in 2001. It monitors international phone calls and e-mails to or from the United States involving people suspected by the government of having terrorist links.

A secret court was established in the late 1970s to grant warrants for such surveillance, but the Justice Department said it can't always wait for the court to act.

The president and his advisers "have determined that the current threat to the United States demands that signals intelligence be carried out with a speed and methodology that cannot be achieved by seeking judicial approval" through traditional channels, Monday's brief said.

The journalists and other plaintiffs lack standing to sue because secrecy considerations mean that "they cannot show, and the government cannot dispute, that the government has intercepted or likely will intercept their communications," the government brief said.

In a brief filed Nov. 14, the ACLU said that the Bush administration's "sweeping theory of executive power would allow the president to violate any law passed by Congress."

"This theory presents a profound threat to our democratic system," it said.

The 6th Circuit Court of Appeals has set a Dec. 18 deadline for other interested groups to file their own briefs in the case.