AT&T Inc. (T) and an Internet advocacy group are waging a privacy battle in federal court that could expose the reach of the Bush administration's secretive domestic wiretapping program.

The Electronic Frontier Foundation said it obtained documents from a former AT&T technician showing that the National Security Agency is capable of monitoring all communications on AT&T's network.

"It appears the NSA is capable of conducting what amounts to vacuum-cleaner surveillance of all the data crossing the Internet, whether that be people's e-mail, Web surfing or any other data," whistle-blower Mark Klein, who worked for the company for 22 years, said in a statement released by his lawyers.

U.S. District Judge Vaughn Walker is considering whether to unseal documents that Klein provided and AT&T wants kept secret. EFF filed the documents under seal as a courtesy to the phone company, but is seeking to unseal them.

The EFF lawsuit, filed in U.S. District Court, seeks to stop the surveillance program that started shortly after the 2001 terror attacks. The suit is based in large part on the Klein documents, which detail secret spying rooms and electronic surveillance equipment in AT&T facilities.

The suit claims AT&T company not only provided direct access to its network that carries voice and data but also to its massive databases of stored telephone and Internet records that are updated constantly.

AT&T violated U.S. law and the privacy of its customers as part of the "massive and illegal program to wiretap and data-mine Americans' communications" without warrants, the EFF alleged.

Klein said the NSA built a secret room at the company's San Francisco central office in 2003, adjacent to a "switch room where the public's phone calls are routed."

One of the documents under seal, Klein said, shows that a device was installed with the "ability to sift through large amounts of data looking for preprogrammed targets."

Other so-called secret rooms were constructed at AT&T sites in Seattle, San Jose, Los Angeles and San Diego, the statement said.

Other documents under seal show that fiber-optic cables from the secret room tapped into WorldNet Internet subscribers, Klein said. The documents also instructed technicians how to connect cables to the secret room. Klein said he was required to connect circuits that fed information to the secret room.

The NSA declined directly to address the lawsuit or Klein's allegations, which covered activities at AT&T Corp. before SBC Communications Inc. bought it and became AT&T Inc. late last year.

"Any discussion about actual or alleged operational issues would be irresponsible as it would give our adversaries insight that would enable them to adjust and potentially inflict harm to the U.S.," NSA spokesman Don Weber said.

Michael Balmoris, an AT&T spokesman, said the San Antonio-based telecommunications company "follows all laws with respect to assistance offered to government agencies." He declined further elaboration, saying AT&T is "not in a position to comment on matters of national security or litigation."

President Bush confirmed in December that the NSA has been conducting the surveillance when calls and e-mails, in which at least one party is outside the United States, are thought to involve Al Qaeda terrorists.

In congressional hearings last week, Attorney General Alberto Gonzales suggested the president could order the NSA to listen in on purely domestic calls without first obtaining a warrant from a secret court established nearly 30 years ago to consider such issues.

He said the administration, assuming the conversation related to Al Qaeda, would have to determine if the surveillance were crucial to the nation's fight against terrorism, as authorized by Congress following the Sept. 11 attacks.