WASHINGTON -- Glenn Greenwald, the Guardian reporter who broke the news of the National Security Agency's mass surveillance programs, said Sunday he will soon disclose new information about the access low-level contractors have to Americans' phone and email communications.

"The NSA has trillions of telephone calls and emails in their databases that they’ve collected over the last several years," Greenwald said on ABC News' "This Week with George Stephanopoulos." "What these programs are, are very simple screens, like the ones that supermarket clerks or shipping and receiving clerks use, where all an analyst has to do is enter an email address or an IP address, and it does two things ... It searches that database and lets them listen to the calls or read the emails of everything that the NSA has stored, or look at the browsing histories or Google search terms that you’ve entered, and it also alerts them to any further activity that people connected to that email address or that IP address do in the future."

"It’s an incredibly powerful and invasive tool, exactly of the type Mr. [Edward] Snowden described," Greenwald added, noting that while the overarching surveillance programs require FISA court approval, analysts can use individual tools and systems to spy on Americans "with no need to go to a court [and] with no need to even get supervisor approval on the part of the analyst."

"These systems allow analysts to listen to whatever emails they want, whatever telephone calls, browsing histories, Microsoft Word documents," Greenwald said.

Sen. Saxby Chambliss (R-Ga.), the top Republican on the Senate Intelligence Committee, disputed the claims during an interview with Stephanopoulos that immediately followed Greenwald's.

“It wouldn’t just surprise me, it would shock me,” Chambliss said.

"What I have been assured of is there is no capability … for anyone without a court order to listen to any telephone conversation or to monitor any email," Chambliss added, noting he visited the NSA headquarters last week and spent time with both high- and low-level officials.

The Republican senator insisted that the agency doesn't monitor emails, and he criticized previous reporting on a program called PRISM, which is said to collect data from nine leading Internet companies, as inaccurate.

"That’s what kind of assures me is that the reporting is not correct, because no emails are monitored now," Chambliss said. "They used to be, but that stopped two or three years ago. So I feel confident that there may have been some abuse, but if it was, it was purely accidental."

The role of private contractors and their access to some of the government's biggest secrets has been a key question raised by the NSA revelations, in addition to the agency's ability to access communications most Americans believe to be private. NSA leaker Edward Snowden obtained a top secret court order about the phone surveillance program during training, the agency's director, Gen. Keith Alexander, said last month.

"The FISA warrant was on a web server that he had access to as an analyst coming into the Threat Operations Center," Alexander said. "It was in a special classified section that as he was getting his training he went to."

Alexander went on to concede that other documents leaked by Snowden were widely available to NSA employees on internal web forums that help employees understand the agency's collection authorities.

Lawmakers like Chambliss and Sen. Dianne Feinstein (D-Calif.), who have defended the NSA programs as critical to national security, told reporters last month they were weighing legislation that would limit the access federal contractors have to highly classified information.

Civil liberties advocates in Congress, on the other hand, have introduced a slew of bills that would curb the federal government's ability to seize data on Americans' phone and electronic communications and declassify the FISA court opinions used to justify such surveillance.

An amendment from Rep. Justin Amash (R-Mich.) that would stop the NSA's collection of phone records was narrowly defeated in the House of Representatives Wednesday, signalling growing concerns among lawmakers over the government's interpretation of the Patriot Act Section 215 and FISA Amendments Act Section 702, under which the programs are considered lawful.

During a hearing on Capitol Hill earlier this month, Rep. Jim Sensenbrenner (R-Wis.), the author of the Patriot Act, threatened to allow Section 215 to expire if the scope of the NSA's surveillance programs goes unchanged.

"Unless you realize you’ve got a problem, that is not going to be renewed," Sensenbrenner said. "There are not the votes in the House of Representatives to renew Section 215. You have to change how you operate Section 215, otherwise in two and a half years you’re not going to have it anymore."

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