Major U.S. telephone carriers refused to answer questions from the Democratic-led Congress about their possible participation in President George W. Bush's warrantless domestic spying program, according to documents released by lawmakers on Monday.

At issue are reports that surfaced last year that some big telephone companies allowed the U.S. government access to millions of telephone records for Bush's anti-terror efforts following the September 11, 2001 attacks on the United States.

Officials from AT&T, Verizon Communications and Qwest Communications International told the House Energy and Commerce Committee they could not discuss specifics about their companies' roles in any such effort.

The phone companies said it would be illegal for them to discuss the kind of program lawmakers were asking about without permission from the Bush administration.

AT&T essentially finds itself caught in the middle of an oversight dispute between the Congress and the executive relating to government surveillance activities, AT&T General Counsel Wayne Watts said in a letter to the committee.

Unfortunately, under current circumstances, we are unable to respond with specificity to your inquiries, Watts added in the letter to the panel headed by Rep. John Dingell, a Michigan Democrat.

Bush has demanded retroactive immunity from liability for telecommunication firms that participated in warrantless surveillance as part of any new bill to revise the laws governing the tracking of suspected enemy targets.

House Democratic leaders have refused, saying that the administration must first explain what these firms did before they will even consider granting immunity.

The phone companies' responses to Dingell were sent to the committee on Friday.

The companies said they had policies in place to protect customers' privacy, but also said federal law authorized them to help the government investigate criminals and terrorists.

Verizon said phone companies had been targeted in a number of class action lawsuits filed after the government program was revealed in news reports.

In the context of this litigation, we have been informed by the Department of Justice that we cannot confirm or deny Verizon's role (if any) in the alleged programs, said Verizon executive Randal Milch.

Democrats vowed to push the administration for answers.

I look forward to meeting with representatives of the administration in short order, and I am hopeful that they will be forthcoming with the information Congress needs to properly evaluate this program, Dingell said.

Also on Monday, House Judiciary Chairman John Conyers said he had sent a letter to administration officials asking for details about potentially unlawful surveillance activities before 9-11 and allegations that the government had retaliated against Qwest earlier for refusing to participate in the surveillance program.

Former Qwest chief executive Joseph Nacchio refused the government's request up until he left the company in 2002, his lawyer has said.

In his request to the phone companies earlier this month, Dingell asked them to describe how government requests for customer information are made and how the records are disclosed. He also asked if the government tried to install equipment on phone networks to intercept Internet traffic or presented a subpoena ordering the companies to install or permit such equipment.

The 1978 Foreign Intelligence Surveillance Act requires the government to obtain orders from a secret FISA court to conduct surveillance of suspected terrorists in the United States.

After the September 11 attacks, Bush authorized the interception without warrants of communications between people in the United States and others overseas if one had suspected ties to terrorists. Critics charge that program violated the FISA law, but Bush argued he had wartime powers to do so.

In January, Bush put the program under the supervision of the FISA court. Terms of the oversight have not been made public. In August Congress, under pressure from Bush, expanded the power of federal authorities to conduct warrantless surveillance in the tracking of enemy targets.

Democrats want to tighten that law with additional oversight by Congress and the secret court created by FISA.

Michigan Security George W. Bush