The National Security Agency is scheduled to end its dragnet collection of data on phone calls that use domestic carriers Saturday night — the most significant change in U.S. intelligence-gathering since Edward Snowden revealed details of the agency's programs two years ago.
Under the Patriot Act approved by Congress after the attacks of Sept. 11, 2001, the NSA had been permitted to gather records about phone calls and hunt through them to discover connections to al-Qaida and other groups.
The legal authority for that system expires Saturday. Under a new law, the NSA must ask phone companies for records on a case-by-case basis. That gives the agency access to a greater volume of phone records than before.
The Office of the Director of National Intelligence said Friday that the new program limits the data collected to "the greatest extent reasonably practicable."
The end of the program is a victory for Snowden, a former NSA contractor, and his supporters, who say the NSA has too much power to gather data on the everyday lives of Americans. While the documents he released to reporters pushed the government to re-evaluate its approach to spying, they are now more than two years old, and there are already signs the NSA has changed its methods.
Alex Abdo, an attorney with the American Civil Liberties Union, said he is concerned that the Snowden documents provided only a brief glimpse at how the nation's intelligence agencies operate.
"That information becomes more and more stale with every day that passes," he said.
In the most controversial program revealed by Snowden, the NSA collected what it called telephony metadata — records of numbers dialed, times and lengths of calls — in an effort to identify communications among terrorists. Officials say the agency did not eavesdrop on the calls themselves.
Official reviews of the program concluded that it had not helped uncover a single terror plot and otherwise offered few benefits.
Privacy activists expect a tougher fight as they seek limits on programs that have been shown to be important intelligence-gathering tools.
Abdo said the expiration of the program on Saturday still could serve as an important reminder that a majority in Congress can be assembled to pass changes to the legal authorities the NSA relies on.
"The ending of the phone records program may in the future seem to be more a symbolic victory, given it was the first major concession the intelligence agencies had to make," he said.
Rep. C.A. Dutch Ruppersberger, who was the top Democrat on the House Intelligence Committee when the Snowden stories started to appear, called the former contractor a traitor. But he said the new program will restore confidence in the NSA without harming national security.
"I think we have the balance right," he said. "The process that we had is being replaced by a more tailored, narrow process that still lets the government track terrorist suspects."
But in the wake of the attacks in Paris, some lawmakers and presidential candidates have called for the old system to be continued.
Sen. Tom Cotton introduced legislation last week to reauthorize and extend the program.
"If we take anything from the Paris attacks, it should be that vigilance and safety go hand-in-hand," the Arkansas Republican said in a statement. "We should allow the Intelligence Community to do their job and provide them with the tools they need to keep us safe."
The Obama administration supported the change to the NSA program. The Office of the Director of National Intelligence said the shift balances privacy interests and security.
"The Intelligence Community has fulfilled an important Presidential commitment that allows national security professionals to retain the capabilities necessary to continue protecting the country, while strengthening the civil liberties protections that the American people cherish," the office said in a blog post.
While some politicians work to reauthorize the old system, the NSA's lawyers and technologists have continued to develop new ways to collect information.
Documents released under after a Freedom of Information lawsuit was filed by The New York Times show how the agency started piecing together sources to fill in gaps left after a program that collected information about Americans' emails was ended.
Stephen Vladeck, a law professor at American University, said those new details show how the NSA pushes to get data by finding novel ways of interpreting the law.
"We're not going to see the sea change that many expected after and in light of the Snowden disclosures," he said. "But maybe we'll at least see a more skeptical [Foreign Intelligence Surveillance Court] in light of the lessons learned over the past 21/2 years."
The intelligence community has said it will be more transparent about its activities. The law that ended the old phone data program included a number of sunlight provisions.
On Wednesday, the surveillance court named five advisers whom judges can ask to provide an outside view on legal questions presented by intelligence agencies, a step required by the law.