NSA Begins Dismantling Phone Data Collection Program

— -- The National Security Agency has begun "winding down" the once top-secret bulk collection of Americans' phone records after Congress failed to renew or change the program before a holiday recess, a senior administration official told ABC News.

"We've said for the past several days that the wind-down process would need to begin yesterday if there was no legislative agreement. That process has begun," the official said.

The government has relied on Section 215 of the Patriot Act, which expires at midnight on May 31, to authorize collection of telephone metadata for all U.S. calls. That data was said to include phone numbers and duration of a call, but not the content of the call or any other personally identifying information.

Former NSA contractor Edward Snowden revealed the existence of the phone surveillance program with his leaked cache of documents in 2013.

Lawmakers left town for a week-long holiday break without addressing the program as its expiration looms.

The Obama administration did not seek renewal of the bulk collection program, instead proposing that phone companies retain the records and make them available for case-by-case review by the government with a court order. A bipartisan version of that proposal -- the USA Freedom Act -- passed the House of Representatives earlier this month but was blocked in a late-night vote in the Senate.

Defenders of the phone surveillance program insist that ending it will hamper the FBI and NSA in their pursuit of suspected terrorists and spies, though there is little evidence it has been directly responsible for any thwarted plots.

The Senate also failed to advance a short-term extension of the program to allow more time to negotiate a compromise.

Lawmakers will have just 8 hours to resolve their differences over the phone program and other expiring provisions of the PATRIOT Act, which is widely seen as a critical tool for law enforcement, when they return at 4 pm on Sunday, May 31.