A leaked document lays bare the monumental scope of the government's surveillance of Americans' phone records _ hundreds of millions of calls _ in the first hard evidence of a massive data collection program aimed at combating terrorism under powers granted by Congress after the 9/11 attacks.

At issue is a court order, first disclosed Wednesday by The Guardian newspaper in Britain, that requires the communications company Verizon to turn over on an “ongoing, daily basis” the records of all landline and mobile telephone calls of its customers, both within the U.S. and between the U.S. and other countries. Intelligence experts said the government, though not listening in on calls, would be looking for patterns that could lead to terrorists _ and that there was every reason to believe similar orders were in place for other phone companies.

The disclosure comes at a particularly inopportune time for the Obama administration. The president already faces questions over the Internal Revenue Service's improper targeting of conservative groups, the seizure of journalists' phone records in an investigation into who leaked information to the media, and the administration's handling of the terrorist attack in Libya that left four Americans dead.

At a minimum, it's all a distraction as the president tries to tackle big issues like immigration reform and taxes. And it could serve to erode trust in Obama as he tries to advance his second-term agenda and cement his presidential legacy.

One outraged senator was Ron Wyden. He said, “When law-abiding Americans make phone calls, who they call, when they call and where they call is private information. As a result of the discussion that came to light today, now we're going to have a real debate.”

But Sen. Lindsay Graham said Americans have no cause for concern. “If you're not getting a call from a terrorist organization, you've got nothing to worry about,” he said.

At issue is a court order, first disclosed by The Guardian newspaper in Britain, that requires Verizon to turn over, on an “ongoing, daily basis,” records of all landline and mobile telephone calls of its customers, both within the U.S. and between the U.S. and other countries. Intelligence experts said there was every reason to believe that similar orders were in place for other phone companies.

Senate Intelligence Committee Chairwoman Dianne Feinstein said the order was a three-month renewal of an ongoing practice that is supervised by federal judges who balance efforts to protect the country from terror attacks against the need to safeguard Americans' privacy. The surveillance powers are granted under the post-9/11 Patriot Act, which was renewed in 2006 and again in 2011.

While the scale of the program might not have been news to some congressional leaders, the disclosure offered a public glimpse into a program whose breadth is not widely understood. Sen. Mark Udall, who serves on the Intelligence Committee, said it was the type of surveillance that “I have long said would shock the public if they knew about it.”

The public is now on notice that the government has been collecting data _ even if not listening to the conversations _ on every phone call every American makes, a program that has operated in the shadows for years, under President George W. Bush, and continued by President Barack Obama.

“It is very likely that business records orders like this exist for every major American telecommunication company, meaning that if you make calls in the United States the NSA has those records,” wrote Cindy Cohn, general counsel of the nonprofit digital rights group Electronic Frontier Foundation, and staff attorney Mark Rumold, in a blog post.

Without confirming the authenticity of the court order, White House spokesman Josh Earnest said such surveillance powers are “a critical tool in protecting the nation from terror threats,” by helping officials determine if people in the U.S. who may have been engaged in terrorist activities have been in touch with other known or suspected terrorists.

Privacy advocates said the scope of the program was indefensible.

“This confirms our worst fears,” said Alexander Abdo, a staff attorney with the American Civil Liberties Union's National Security Project. “If the government can track who we call,” he said, “the right to privacy has not just been compromised _ it has been defeated.”

Rep. Jim Sensenbrenner, who sponsored the USA Patriot Act that governs the collection, said he was “extremely troubled by the FBI's interpretation of this legislation.”

Attorney General Eric Holder sidestepped questions about the issue during an appearance before a Senate subcommittee, offering instead to discuss it at a classified session that several senators said they would arrange.

The Verizon order does not authorize snooping into the content of phone calls. But with millions of phone records in hand, the NSA's computers can analyze them for patterns, spot unusual behavior and identify “communities of interest” _ networks of people in contact with targets or suspicious phone numbers overseas.

Verizon Executive Vice President and General Counsel Randy Milch, in a blog post, said the company isn't allowed to comment on any such court order.

The company listed 121 million customers in its first-quarter earnings report this April _ 98.9 million wireless customers, 11.7 million residential phone lines and about 10 million commercial lines.

The NSA had no immediate comment. The agency is sensitive to perceptions that it might be spying on Americans. It distributes a brochure that pledges the agency “is unwavering in its respect for U.S. laws and Americans' civil liberties _ and its commitment to accountability.” (AP)