"These programs are within the law," Feinstein, D-California, told ABC's "This Week." And Rep. Mike Rogers, the chairman of the House Intelligence Committee, told ABC, "The inflammatory nature of the comments does not fit with what Dianne and I know this program really does."
"The instances where this has produced good -- has disrupted plots, prevented terrorist attacks -- is all classified," said Rogers, R-Michigan. "That's what's so hard about this."
Clapper: Programs authorized
Clapper's office declassified some details of the programs, which it said were "conducted under authorities widely known and discussed, and fully debated and authorized by Congress."
It said PRISM was created in 2008, targets "foreign targets located outside the United States" and gets reviewed by the administration, Congress and judges. And Rogers told reporters Sunday that "there is not a target on Americans."
Surveillance concerns 'fanciful,' Britain says
But Greenwald, the lead author of the Guardian pieces, told ABC's "This Week" that Americans need an "open, honest debate about whether that's the kind of country that we want to live in."
"These are things that the American people have a right to know," said Greenwald, a lawyer and civil liberties advocate. "The only thing being damaged is the credibility of political officials and the way they exercise power in the dark."
Sen. Mark Udall, D-Colorado, who has long called for greater transparency in how the government collects data on Americans, said the legal authority should be reopened for debate after last week's disclosures.
"Maybe Americans think this is OK, but I think the line has been drawn too far toward 'we're going to invade your privacy,' versus 'we're going to respect your privacy,'" Udall told CNN's "State of the Union."
The Obama administration is already under fire following revelations the Justice Department seized two months of phone records from Associated Press reporters and editors as part of an investigation into leaks of classified information.
'I do not expect to see home again'
The Guardian reported that Snowden grew up in North Carolina and Maryland. He joined the Army in 2003 but was discharged after breaking both his legs in a training accident. He never completed a high-school diploma but learned computer skills at a community college in Maryland.
He started his career as a security guard for an NSA facility at the University of Maryland, then went to work for the CIA in Internet security. In 2009, he got the first of several jobs with private contractors that worked with the NSA.
In a statement issued Sunday afternoon, Booz Allen said Snowden had worked for the company for less than three months. The news that he had leaked American secrets was "shocking" and if true, "represents a grave violation of the code of conduct and core values of our firm," the company said.
Snowden told the Guardian that he left for Hong Kong on May 20 without telling his family or his girlfriend what he planned.
"I do not expect to see home again," he told the paper, acknowledging the risk of imprisonment over his actions.
"You can't come up against the world's most powerful intelligence agencies and not accept the risk," he said. "If they want to get you, over time they will."