Correction: A previous version of this story incorrectly stated the National Security Agency had been able to receive information including customers’ names, addresses and financial information through a court order. This version has been corrected.

The National Security Agency appears to be collecting the telephone records of tens of millions of American customers of Verizon, one of the nation’s largest phone companies, under a top-secret court order issued in April.

The order appears to require a Verizon subsidiary to provide the NSA with daily information on all telephone calls by its customers within the United States and from foreign locations into the United States.

The order, which was signed by a judge from the secret court that oversees domestic surveillance, was first reported on the Web site of the Guardian newspaper. The Web site reproduced a copy of the order, which two former U.S. officials told The Washington Post appears to be authentic.

A senior Obama administration official said Thursday that the purported order “does not allow the government to listen in on anyone’s telephone calls” but relates only to “metadata, such as a telephone number or the length of a call.” The official said such information “has been a critical tool in protecting the nation from terrorist threats to the United States.”

The official added that “all three branches of government are involved in reviewing and authorizing intelligence collection” under the secret court, and Congress “is regularly and fully briefed” on how the information is used.

If the document published by the Guardian is genuine, it could represent the broadest surveillance order known to have been issued. It also would confirm long-standing suspicions of civil liberties advocates about the sweeping nature of U.S. surveillance through commercial carriers under laws passed after the Sept. 11, 2001, terrorist attacks.

An expert in this aspect of the law said Wednesday night that the order appears to be a routine renewal of a similar order first issued by the same court in 2006. The expert, who spoke on the condition of anonymity to discuss sensitive issues, said that the order is reissued routinely every 90 days and that it is not related to any particular investigation by the FBI or any other agency.

The expert referred to such orders as “rubber stamps” sought by the telephone companies to protect themselves after the disclosure in 2005 that widespread warrantless wiretaps could leave them liable for damages.

The order falls under Section 215 of the Patriot Act, which authorizes the government to make broad demands on telephone carriers for information about calls. In this case, the order requires Verizon to provide “ongoing, daily” information about “all call detail records . . . created by Verizon for communications between the United States and abroad; or wholly within the United States, including local telephone calls.”

The FBI, which apparently sought the order, declined to comment. Spokesmen for Verizon and the court also declined to comment.

But civil liberties groups were quick to criticize the sweeping nature of the order.

“This is a truly stunning revelation,” said Elizabeth Goitein, co-director of the Liberty and National Security Program at the Brennan Center for Justice. “This suggests that the government has been compiling a comprehensive record of Americans’ associations and possibly even their whereabouts.”

The Center for Constitutional Rights, which has sued the government over its surveillance prac­tices, said in a statement Wednesday night that the order “requires no level of suspicion and applies to all Verizon subscribers anywhere in the U.S. It also contains a gag order prohibiting Verizon from disclosing information about the order to anyone other than their counsel.”

Former vice president Al Gore called the order “obscenely outrageous.” In a tweet posted Wednesday night, he said: “In digital era, privacy must be a priority. Is it just me, or is secret blanket surveillance obscenely outrageous?”

The order also seems to confirm fears expressed by Sens. Ron Wyden (D-Ore.) and Mark Udall (D-Colo.). In a letter to Attorney General Eric H. Holder Jr. last year, they said, “We believe most Americans would be stunned to learn the details of . . . these secret court opinions. As we see it, there is now a significant gap between what most Americans think the law allows and what the government secretly claims the law allows.”

Government officials have defended the broad surveillance powers, saying that the information has been vital in uncovering and disrupting terrorist plots. They also say that the surveillance has operated under the provisions of the Patriot Act and other laws.

The court order, good for three months, requires Verizon to hand over to the NSA, the world’s largest spy agency, comprehensive communications-routing information, including but not limited to numbers dialed and received and length and time of calls. The order does not tell Verizon to provide customers’ name and addresses, financial information, or any information about the content of the calls.

The “business records” order, issued by the Foreign Intelligence Surveillance Court, does not require a showing of probable cause to believe that the targets are agents of a foreign power. Rather, all that is required is a showing that “there are reasonable grounds to believe” that the tangible things sought are “relevant to an authorized investigation . . .to obtain foreign intelligence information . . . or to protect against international terrorism or clandestine intelligence activities.”

“Tell me how all of the metadata of Americans’ domestic conversations can be relevant to an authorized foreign intelligence or international terrorism investigation,” said Goitein, who was counsel to then-Sen. Russell Feingold (D-Wis.), a Senate Judiciary Committee member who left Congress in January 2011.

Feingold raised concerns about the government’s secret interpretation of Section 215, a concern picked up by Wyden and Udall in recent years. These lawmakers have pressed the Justice Department and the court to release redacted versions of their opinions so that Americans can understand the full extent of the government’s surveillance authorities.

The order does not specify whether location data, such as cell tower or GPS coordinates, also are being turned over. But even without such data, the NSA is still gathering massive amounts of information that can give a detailed picture of people’s networks of associates and who they are communicating with, when and for how long.

“It’s the kind of networking information that can be very important in legitimate terrorism investigations but that the government has no business knowing about ordinary law-abiding Americans,” Goitein said.

Privacy advocates said they believed that the NSA must be collecting such information from all the large carriers and that this practice has been going onfor years.After the September 2001 terrorist attacks, the Bush administration began a secret NSA program for the bulk collection of Americans’ call records as part of a broader counter-terrorism effort that included the wiretapping of Americans’ international phone communications with suspected terrorists without a warrant. The latter effort was put under secret court supervision in 2007. But until now, there had been no evidence that the call records program, whose disclosure by USA Today in 2006 created an uproar, continued under the Obama administration.