The controversy has prompted members of Congress to put growing pressure on U.S. intelligence agencies to improve their transparency.

The NSA insists that it only eavesdrops on or collects phone content from Americans’ overseas calls, and then only if it has a documented foreign intelligence purpose, such as counterterrorism, and obtains approval from a secret court. The agency’s director, Army Gen. Keith Alexander, told a House of Representatives hearing last month that the programs and other intelligence have protected Americans from terrorist attacks “in a way that does not compromise the privacy and civil liberties of our citizens.”

National intelligence chief James Clapper, in a recent NBC television interview, called it “ludicrous” to suggest that the government wants to listen to the private phone calls of everyday Americans.

During the House hearing, Gen. Alexander told Congress that the agency’s “partnerships” with telecom and Internet companies have helped disrupt more than 50 terrorist attacks over the last 12 years.

Deputy Attorney General Jim Cole testified that the NSA doesn’t know the identities of Americans whose phone numbers are collected and only gets access to call content when investigators have found enough evidence to target a foreign terrorism suspect. So-called “metadata” about billions of emails is treated similarly, officials said.

But even as the Justice Department pursued Snowden on espionage charges from Hong Kong to Moscow, The Guardian reported that the British spy agency GCHQ has tapped into more than 200 cables carrying the world’s phone calls and Internet traffic and is sharing the data with the NSA. By May 2012, it said, 250 NSA analysts had been assigned to help comb through the mountain of data.

Digitized records of calls over Google Voice, Skype and other “voice over Internet” systems, many of them to points overseas, would be among the records.

NSA spokeswoman Judith Emmel said that the “NSA does not ask its foreign partners to undertake any intelligence activity that the U.S. government would be legally prohibited from undertaking itself.”

NSA’s doubters point, in particular, to the agency’s push to build the massive data center in Bluffdale, Utah, whose storage capacity will be measured in the highest metric now used – “yodabytes,” named for Yoda, the “Star Wars” character.

Thomas Drake, a former NSA senior executive who challenged the data collection for several years, said the agency’s intent seems obvious.

“One hundred million phone records?” he asked in an interview. “Why would they want that each and every day? Of course they’re storing it.”

Drake, who fears that NSA chief Alexander is building “extraordinary power,” wound up as the fourth American to face charges under the Espionage Act after he blew the whistle on a wasteful NSA data-collection system. His prosecution, which Drake alleges was both retaliatory and an attempt to silence other potential leakers, eventually crumbled.

Lending credence to his worries, The Guardian’s latest report quoted a document in which Alexander purportedly remarked during a 2008 visit to an NSA intercept station in Britain: “Why can’t we collect all the signals all the time?”