ASHINGTON, Sept. 14 — The political pressure to do something — anything — to ensure that there is never a repeat of this week's terrorist attacks is immense on Capitol Hill. And civil liberties advocates are watching with quiet concern.
Across the political spectrum, lawmakers are arguing that the United States has entered a new and more dangerous era that demands heightened security measures, including armed guards on commercial airliners and greater surveillance powers for federal agents.
Senator Trent Lott, the Republican leader, declared the day after the attacks: "When you are at war, civil liberties are treated differently. We cannot let what happened yesterday happen in the future."
The attitude shift is not confined to conservative Republicans. Representative Barney Frank, Democrat of Massachusetts, said, "The general assumption in this country is freedom and individual privacy." But he added, "When conditions turn adverse, you respond to them."
In his case, Mr. Frank said, "I think I will be more supportive of more freedom for electronic surveillance than I was before, and I think more of an armed presence on airplanes."
Civil liberties groups, while initially muted as the nation grieved, were just beginning to voice their concerns today.
"It's very important at a time of crisis to reaffirm national principles, national ideals," said Marc Rotenberg, director of the Electronic Privacy Information Center. "I certainly understand the sense of frustration and tragedy — my own family has been touched by what's happened this week — but it would be an enormous cost to severely limit American freedoms."
Some advocates were dismayed by a proposal the Senate approved on Thursday night that would, among other things, make it easier for federal law enforcement to wiretap computers.
Senator Jon Kyl, Republican of Arizona, who is a member of the Senate Intelligence Committee, declared: "We are in a race to the finish line with agents of terror. Will we enhance our security and defenses before they are able to strike again?"
But Barry Steinhardt, associate director of the American Civil Liberties Union, said today, "This amendment proposes significant and dangerous changes to our wiretapping laws and should not have been adopted literally in the middle of the night without debate or scrutiny."
Civil liberties groups are also concerned about ideas like expanding use of face-recognition technology, which allows security cameras tied to computers to search a crowd for criminals.
Representative Martin T. Meehan, Democrat of Massachusetts, said: "I don't think we've done a good enough job in this country utilizing the technology available, like facial recognition technology. We need to make greater investments there."
Mr. Meehan, who was interviewed while the Capitol was being evacuated on Thursday night, also felt that the nation's attitudes had fundamentally changed after the attacks. "Given this unspeakable act, Americans will tolerate some restraint on their liberties for the sake of security," he said.
And polling suggests that they are more than willing to make that tradeoff.
With many of these proposals, like face-recognition systems, "we have to really reflect on how much we value privacy," said Walter Dellinger, who served as acting solicitor general in the Clinton administration.
"With terrorism, our only defense might be infiltration and surveillance, so we're going to have to choose between security and privacy."
To monitor such proposals from both Congress and the administration in the coming months, a new coalition of civil rights, civil liberties, religious and other organizations is beginning to form, advocates said. Already, such groups were sounding the alarm about the possibility of a backlash and discrimination against Arab-Americans.
In part, such fears are a reaction to history.
"We know what happened post- Pearl Harbor; we know what happens when you have these national security situations," said Ralph Neas, president of People for the American Way, a liberal rights group, recalling the wartime relocation and internment of Japanese- Americans after the 1941 attack. "Many times," Mr. Neas said, "there are overreactions, not based on fact or careful analysis, that lead to a violation of the Constitution."
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