A U.S. government official, who lacked authorization to speak for the record, said that Alexander’s comment was merely “a quip taken out of context.”

NSA officials say the leaks have undermined their attempt to cloak their operations to avoid tipping off terrorists to their sources and methods. But in a debate that touches the vast majority of Americans, the agency hasn’t won many points for candor.

The NSA kept secret for more than four years that it was conducting warrantless wiretaps on overseas callers as part of its hunt for al Qaida members and other terrorists.

Last week, the agency removed from its website a fact sheet describing how it interpreted its authority under a post-Sept. 11, 2001, USA PATRIOT Act provision through which it’s collected Internet records – after members of Congress pointed to an inaccurate statement. Wyden and Udall, who have led congressional scrutiny of the agency, wrote Alexander that the error, which is classified, was “significant, as it portrays protections for Americans’ privacy as being significantly stronger than they actually are.”

The two senators, members of the Senate intelligence committee, chided Alexander that such inaccuracies “can decrease public confidence in the NSA’s openness.”

In a separate letter to spy chief Clapper, Wyden and 25 other senators lamented having learned through an unauthorized disclosure that the Patriot Act had been “secretly reinterpreted to allow the government to collect the private records of large numbers of ordinary Americans.”

In addition, Clapper dashed off an apology letter to the Senate after acknowledging in a recent NBC television interview that he gave “the least untruthful” answer he could in denying in sworn testimony in March that the NSA had collected huge caches of data on Americans.

George Washington’s Turley called Clapper’s statement an admission of a lie. He chastised members of the Senate intelligence committee – led by Democratic Chairwoman Dianne Feinstein of California and ranking Republican Saxby Chambliss of Georgia – for failing to seek a Justice Department perjury investigation, especially since they knew the extent of the surveillance program.

“They didn’t give Roger Clemens a choice: Did you speak truthfully or just get as close as you could?” Turley said, referring to the former New York Yankees pitching star who had to win acquittal by a jury to fend off charges that he lied to Congress in denying steroid use.

Clapper appears to have played a game of semantics over the meaning of the word “collect.” James Bamford, author of “The Shadow Factory” and two other books about the NSA, said that under the agency’s formal definition, an intercept only occurs “when a communication becomes understandable to a human being.”

The Patriot Act gave intelligence and law enforcement authorities a huge tool for looking at phone and Internet data to help identify terror networks. It authorized them to obtain orders from the secret Foreign Intelligence Surveillance Court that directed telecom and Internet giants such as Google, Verizon, AT&T, Facebook, Microsoft and Apple to share email and phone data.

Effectively, the law enabled the intelligence agencies to keep up with technological leaps that have transformed the world of surveillance. Nearly all personal data now moves over fiber-optic cables, each of whose tiny filaments can use pulsating flashes of light to transmit up to 100 billion bits of data per second.

Major phone carriers currently do not store digital recordings of phone calls, except for those occurring under court-ordered wiretaps, said a former technology chief for a major telecom company, who spoke on condition of anonymity to avoid harming relationships.

That means that the NSA only could collect the content of calls by flagging targets going forward or by capturing data and storing some or all of it.

Jim Hayes, head of the California-based Fiber Optic Association who once wrote a classified paper on how to tap into a cable, said that it would be relatively easy for the agency to copy data from a cable.

One former U.S. security consultant, who spoke on condition of anonymity to protect his connections to government agencies, told McClatchy he has seen agency-installed switches across the country that draw data from the cables.

“Do I know they copied it? Yes,” said the consultant. “Do I know if they kept it? No.”

Spokesmen for phone and Internet providers Verizon and AT&T, both of which have been gagged by the national security statutes from discussing their court-ordered assistance to the NSA, declined to comment.

Tish Wells of the Washington Bureau contributed.