A suit against AT&T over alleged cooperation with government wiretapping should be dismissed because hearing it would mean exposing information that would help Al-Qaeda, the U.S. Department of Justice argued Friday in federal court in San Francisco.

Simply confirming or denying that such surveillance takes place could embolden terrorists by letting them know which forms of communication are monitored and which are not, Assistant Attorney General Peter Keisler told Judge Vaughn Walker of the U.S. District Court for the Northern District of California.

The civil liberties group Electronic Frontier Foundation (EFF) in January sued AT&T on behalf of the carrier's customers, alleging it diverts traffic from its fiber-optic lines to the National Security Agency (NSA) as part of an illegal antiterrorist surveillance program. The class-action suit, one of several in the works, followed press reports last year about several major carriers providing data for broad domestic spying initiatives.

Judge Walker heard arguments Friday on motions by the government and AT&T to have the case dismissed, as well as on unsealing evidence and including AT&T as a defendant. He did not rule Friday or indicate when he may reach a decision. Both sides said they would appeal if the decision goes against their wishes.

Attorneys for AT&T said the carrier did nothing wrong but in any case could not be sued for complying with an authorized government search. It would be up to EFF to establish that there was no legal certification for the surveillance program, said Bradley Berenson of the law firm Sidley Austin Brown & Wood, a former associate White House counsel under President George Bush.

If the executive branch of government did authorize the NSA wiretap, it would be up to Congress, not AT&T or the courts, to determine whether that program was legal or not, Berenson said. Congress has had the chance to probe domestic spying programs started in the wake of the Sept. 11, 2001, terrorist attacks, he said. Michael Hayden, who led the NSA when Bush ordered the spying, was confirmed last month as director of the Central Intelligence Agency, a sign that Congress approved of the efforts, Berenson said.

EFF argued there are tight restrictions on wiretaps and AT&T had a responsibility to ensure the legality of a search it was being asked to assist in.

Also at the hearing, EFF and attorneys for media organizations called for key documents in the case, now mostly sealed, to be made public. AT&T and the government said the exposure so far of evidence apparently related to the case, such as documents from former AT&T engineer Mark Klein, doesn't argue for unsealing all the documents.

EFF also sought to include AT&T, which became the new parent company of AT&T last year after its merger with SBC Communications, as a defendant in the case. The judge did not rule on either motion Friday.