SAN FRANCISCO -- The federal government is urging an appeals court to dismiss a lawsuit challenging President Bush's domestic eavesdropping program, warning that disclosure of such activities could compromise national security.

"The suit's very subject matter -- including the relationship, if any, between AT&T and the government in connection with the secret intelligence activities alleged by plaintiffs -- is a state secret," the Justice Department argued in court papers.

The documents were filed late Friday and released Monday by the Electronic Frontier Foundation, which brought the suit. It accuses AT&T Inc. of illegally making communications on its networks available to the National Security Agency without warrants, and challenges Bush's assertion that he could use his wartime powers to eavesdrop on Americans without a warrant.

The National Security Agency had conducted the surveillance without a court warrant until January, when the Foreign Intelligence Surveillance Court began overseeing the program.

The court filings on Friday are part of the government's appeal of U.S. District Judge Vaughn Walker's decision last year to keep the Electronic Frontier Foundation's lawsuit alive. Walker ruled that warrantless eavesdropping has been so widely reported that there appears to be no danger of spilling secrets.

The 9th U.S. Circuit Court of Appeals is to rule on whether Walker was correct to allow the case to proceed to trial. The court has not said when it will rule.

AT&T, too, is seeking dismissal of the case and filed a brief that echoes the language in the government's.

Both the government and the telecommunications giant rely heavily upon a declaration last year by John Negroponte, then-director of national intelligence, who said revealing information about the program could "cause exceptionally grave damage to the national security of the United States."

The Electronic Frontier Foundation's "standing" to bring such a lawsuit cannot be established without disclosing "state secrets," the government and the company argue.

The plaintiffs do not have grounds to press such claims unless they can show "that AT&T in fact assisted in the alleged program, and that plaintiffs' own communications were in fact intercepted and accessed by the government under the alleged program," AT&T argued.

Moreover, the government said, the very merits of the case and whether it should be dismissed cannot be resolved in court because a "state secrets privilege" does not allow it.

The government also filed a classified brief Friday that was not released publicly.