The leaders of the Senate and House Intelligence committees defended the National Security Agency's phone and internet surveillance programs revealed last week, saying that the programs are "within the law" and have been critical in thwarting potential terrorist attacks.

Senate Intelligence Committee Chair Sen. Dianne Feinstein, D-Calif., said on "This Week" Sunday that the NSA phone surveillance program revealed in reports last week is limited in scope to viewing phone records, not listening to private conversations, while reiterating that court orders are required for further information.

"The program is essentially walled off within the NSA. There are limited numbers of people who have access to it," Feinstein said on "This Week." "The only thing taken, as has been correctly expressed, is not content of a conversation, but the information that is generally on your telephone bill, which has been held not to be private personal property by the Supreme Court. If there is strong suspicion that a terrorist outside of the country is trying to reach someone on the inside of the country, those numbers then can be obtained. If you want to collect content on the American, then a court order is issued."

"The National Security Agency does not listen to Americans' phone calls and it is not reading Americans' emails. None of these programs allow that," added Rep. Mike Rogers, R-Mich., chair of the House Intelligence Committee.

Both Feinstein and Rogers said that the phone and internet surveillance programs has been instrumental in stopping terrorist attacks, citing the 2009 terror plot by Najibullah Zazi, the Colorado resident who was arrested in Sept. 2009 after plotting to bomb the New York subway system. Feinstein said the program also helped to track the case of David Headley, a Pakistani-American who traveled to Mumbai to scope the Taj Mahal Hotel for an attack.

"I can tell you, in the Zazi case in New York, it's exactly the program that was used," Rogers said, later adding, "I think the Zazi case is so important, because that's one you can specifically show that this was the key piece that allowed us to stop a bombing in the New York Subway system."

Feinstein said the shadow of the Sept. 11 terrorist attacks still loom in her mind, and that strong intelligence from the type of surveillance conducted by the NSA is needed to prevent future attacks.

"I flew over World Trade Center going to Senator [Frank] Lautenberg's funeral, and in the distance was the Statue of Liberty. And I thought of those bodies jumping out of that building, hitting the canopy," Feinstein said. "Part of our obligation is keeping Americans safe. Human intelligence isn't going to do it, because you can't - it's a different culture. It is a fanaticism that isn't going to come forward."

Feinstein said she would be open to public hearings on the surveillance programs, and said that the Senate Intelligence Committee has made information on the programs available to all senators. But she noted the difficulty of being fully public without disclosing classified information.

"The instances where this has produced good - has disrupted plots, prevented terrorist attacks - is all classified, that's what's so hard about this," Feinstein said. "So that we can't actually go in there and, other than the two that have been released, give the public an actual idea of people that have been saved, attacks that have been prevented, that kind of thing."

Andrew Harrer/Bloomberg via Getty Images

"If you tell our adversaries and enemies in the counterterrorism fight exactly how we conduct business, they are not going to do business the same ever again," Rogers added. "It makes it more difficult."

Sen. Mark Udall, D-Colo., who has raised warnings about the domestic surveillance methods in recent years, said he hopes the released information will spark debate over the NSA's methods, and will lead to re-opening the Patriot Act to limit the NSA's abilities.

"I think it's an opportunity now to have a discussion about the limits of surveillance, how we create transparency, and above all, how we protect Americans' privacy," Udall said this morning on "This Week." "My main concern is Americans don't know the extent to which they are being surveilled… I think we ought to reopen the Patriot Act and put some limits on the amount of data that the National Security Administration is collecting."

Udall said he did not believe the right balance is being struck currently between privacy and security.

"We do need to remember, we're in a war against terrorists, and terrorism remains a real threat, but I also think we have to cue to the Bill of Rights, and the Fourth Amendment, which prevents unlawful searches and seizures, ought to be important to us," Udall said. "It ought to remain sacred, and there's got to be a balance here. That is what I'm aiming for."

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