WASHINGTON, Dec. 24 - Congressional officials said Saturday that they wanted to investigate the disclosure that the National Security Agency had gained access to some of the country's main telephone arteries to glean data on possible terrorists.

"As far as Congressional investigations are concerned," said Senator Patrick J. Leahy of Vermont, the ranking Democrat on the Judiciary Committee, "these new revelations can only multiply and intensify the growing list of questions and concerns about the warrantless surveillance of Americans."

Members of the Judiciary Committee have already indicated that they intend to conduct oversight hearings into the president's legal authority to order domestic eavesdropping on terrorist suspects without a warrant.

But Congressional officials said Saturday that they would probably seek to expand the review to include the disclosure that the security agency, using its access to giant phone "switches," had also traced and analyzed phone and Internet traffic in much larger volumes than what the Bush administration had acknowledged.

"We want to look at the entire program, an in-depth review, and this new data-mining issue is certainly a part of the whole picture," said a Republican Congressional aide, who asked not to be identified because no decisions had been made on how hearings might be structured.

Current and former government officials say that the security agency, as part of its domestic surveillance program, has gained the cooperation of some of the country's biggest telecommunications companies to obtain access to large volumes of international phone and Internet traffic flowing in and out of the United States.

The agency has traced and analyzed the traffic flow - looking at who is calling whom, where calls originate and end, and other patterns - to gather clues on possible terrorist activities. In cases where security agency supervisors believe they can show a link to Al Qaeda, President Bush has authorized eavesdropping on calls without a warrant within the United States, so long as one end of the phone or e-mail conversation takes place outside the country.

The White House declined to comment Saturday on the security agency program or the use of data-mining, saying it would not discuss intelligence operations.

"The administration will aggressively fight the war on terror in an effort to protect the American people while at the same time upholding the civil liberties of the American people," said Allen Abney, a White House spokesman. "The president is doing both of these things and will continue to do both of these things."

Defenders of the program within the federal government say that the security agency's broad analytical searches and data-mining, combined with actual eavesdropping, are an essential part of detecting and preventing terror attacks.

And they say the president is well within his legal authority to order such programs, because of his inherent constitutional power and because of Congressional authorization in the days after the Sept. 11, 2001, attacks that permitted him to use "all necessary and appropriate force" to fight terrorism.

But civil rights and privacy advocates voiced concerns Saturday about the expanded role of the security agency, which historically has focused almost exclusively on foreign powers in mining for data on American phone lines.

"To the extent that the N.S.A. is collecting information on people who are suspected of no wrongdoing whatsoever, it presents some very critical privacy concerns," said Marcia Hofmann, who leads the government oversight section at the Electronic Privacy Information Center, a group that lobbies for greater privacy rights. "And it shows the need for Congress to put in place real safeguards to prevent the government from abusing this information."

Lisa Graves, senior counsel with the American Civil Liberties Union, said, "There's no data-mining loophole in the Fourth Amendment." Ms. Graves added, "We're seeing an administration that's engaging in a lot of legal hair-splitting to justify behavior that's not authorized by the law."

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