Verizon Communications, the nation's second-largest telecom company, told congressional investigators that it has provided customers' telephone records to federal authorities in emergency cases without court orders hundreds of times since 2005.

The company said it does not determine the requests' legality or necessity because to do so would slow efforts to save lives in criminal investigations.

In an Oct. 12 letter replying to Democratic lawmakers, Verizon offered a rare glimpse into the way telecommunications companies cooperate with government requests for information on U.S. citizens.

Verizon also disclosed that the FBI, using administrative subpoenas, sought information identifying not just a person making a call, but all the people that customer called, as well as the people those people called. Verizon does not keep data on this "two-generation community of interest" for customers, but the request highlights the broad reach of the government's quest for data.

The disclosures, in a letter from Verizon to three Democrats on the House Energy and Commerce Committee investigating the carriers' participation in government surveillance programs, demonstrated the willingness of telecom companies to comply with government requests for data, even, at times, without traditional legal supporting documents. The committee members also got letters from AT&T and Qwest Communications International, but those letters did not provide details on customer data given to the government. None of the three carriers gave details on any classified government surveillance program.

From January 2005 to September 2007, Verizon provided data to federal authorities on an emergency basis 720 times, it said in the letter. The records included Internet protocol addresses as well as phone data. In that period, Verizon turned over information a total of 94,000 times to federal authorities armed with a subpoena or court order, the letter said. The information was used for a range of criminal investigations, including kidnapping and child-predator cases and counter-terrorism investigations.

Verizon and AT&T said it was not their role to second-guess the legitimacy of emergency government requests.

The letters were released yesterday by the lawmakers as Congress debates whether to grant telecom carriers immunity in cases in which they are sued for disclosing customers' phone records and other data as part of the government's post-September 11 surveillance program, even if they did not have court authorization. House Democrats have said that they cannot contemplate such immunity without first understanding the nature of the carriers' cooperation with the government.

"The responses from these telecommunications companies highlight the need of Congress to continue pressing the Bush administration for answers. The water is as murky as ever on this issue, and it's past time for the administration to come clean," said Rep. Edward J. Markey (D-Mass.), who launched the investigation with panel Chairman John D. Dingell (D-Mich.), and Rep. Bart Stupak (D-Mich.).

Congressional Democrats have been largely stymied in their efforts to have the Bush administration disclose the scope and nature of its surveillance and data-gathering efforts after the Sept. 11, 2001, attacks. Revelations have come through press reports, advocacy groups' Freedom of Information Act lawsuits and Justice Department inspector general reports.

In May 2006, USA Today reported that the National Security Agency had been secretly collecting the phone-call records of tens of millions of Americans, using data provided by major telecom firms. Qwest, it reported, declined to participate because of fears that the program lacked legal standing.

Last month, the Electronic Frontier Foundation, a privacy group in San Francisco, obtained records through a Freedom of Information Act lawsuit showing that the FBI sought data from telecom companies about the calling habits of suspects and their associates, the New York Times reported. Neither Qwest nor AT&T answered the lawmakers' question as to whether they had received such requests for information.