The scale of America's surveillance state was laid bare on Thursday as senior politicians revealed that the US counter-terrorism effort had swept up swaths of personal data from the phone calls of millions of citizens for years.

After the revelation by the Guardian of a sweeping secret court order that authorised the FBI to seize all call records from a subsidiary of Verizon, the Obama administration sought to defuse mounting anger over what critics described as the broadest surveillance ruling ever issued.

A White House spokesman said that laws governing such orders "are something that have been in place for a number of years now" and were vital for protecting national security. Dianne Feinstein, the Democratic chairwoman of the Senate intelligence committee, said the Verizon court order had been in place for seven years. "People want the homeland kept safe," Feinstein said.

But as the implications of the blanket approval for obtaining phone data reverberated around Washington and beyond, anger grew among other politicians.

Intelligence committee member Mark Udall, who has previously warned in broad terms about the scale of government snooping, said: "This sort of widescale surveillance should concern all of us and is the kind of government overreach I've said Americans would find shocking." Former vice-president Al Gore described the "secret blanket surveillance" as "obscenely outrageous".

The Verizon order was made under the provisions of the Foreign Intelligence Surveillance Act (Fisa) as amended by the Patriot Act of 2001, passed in the wake of the 9/11 attacks. But one of the authors of the Patriot Act, Republican congressman Jim Sensenbrenner, said he was troubled by the Guardian revelations. He said that he had written to the attorney general, Eric Holder, questioning whether "US constitutional rights were secure".

He said: "I do not believe the broadly drafted Fisa order is consistent with the requirements of the Patriot Act. Seizing phone records of millions of innocent people is excessive and un-American."

The White House sought to defend what it called "a critical tool in protecting the nation from terrorist threats". White House spokesman Josh Earnest said Fisa orders were used to "support important and highly sensitive intelligence collection operations" on which members of Congress were fully briefed.

"The intelligence community is conducting court-authorized intelligence activities pursuant to a public statute with the knowledge and oversight of Congress and the intelligence community in both houses of Congress," Earnest said.

He pointed out that the order only relates to the so-called metadata surrounding phone calls rather than the content of the calls themselves. "The order reprinted overnight does not allow the government to listen in on anyone's telephone calls," Earnest said.

"The information acquired does not include the content of any communications or the name of any subscriber. It relates exclusively to call details, such as a telephone number or the length of a telephone call."

But such metadata can provide authorities with vast knowledge about a caller's identity. Particularly when cross-checked against other public records, the metadata can reveal someone's name, address, driver's licence, credit history, social security number and more. Government analysts would be able to work out whether the relationship between two people was ongoing, occasional or a one-off.

The disclosure has reignited longstanding debates in the US over the proper extent of the government's domestic spying powers.

Ron Wyden of Oregon, a member of the Senate intelligence committee who, along with Udell, has expressed concern about the extent of US government surveillance, warned of "sweeping, dragnet surveillance". He said: "I am barred by Senate rules from commenting on some of the details at this time, However, I believe that when law-abiding Americans call their friends, who they call, when they call, and where they call from is private information.

"Collecting this data about every single phone call that every American makes every day would be a massive invasion of Americans' privacy."

'Beyond Orwellian'

Jameel Jaffer, deputy legal director at the American Civil Liberties Union, said: "From a civil liberties perspective, the program could hardly be any more alarming. It's a program in which some untold number of innocent people have been put under the constant surveillance of government agents.

"It is beyond Orwellian, and it provides further evidence of the extent to which basic democratic rights are being surrendered in secret to the demands of unaccountable intelligence agencies."

Under the Bush administration, officials in security agencies had disclosed to reporters the large-scale collection of call records data by the NSA, but this is the first time significant and top-secret documents have revealed the continuation of the practice under President Obama.

The order names Verizon Business Services, a division of Verizon Communications. In its first-quarter earnings report, published in April, Verizon Communications listed about 10 million commercial lines out of a total of 121 million customers. The court order, which lasts for three months from 25 April, does not specify what type of lines are being tracked. It is not clear whether any additional orders exist to cover Verizon's wireless and residential customers, or those of other phone carriers.

Fisa court orders typically direct the production of records pertaining to a specific, named target suspected of being an agent of a terrorist group or foreign state, or a finite set of individually named targets. The unlimited nature of the records being handed over to the NSA is extremely unusual.

Senators Dianne Feinstein, chairman of the Senate intelligence committee, and Saxby Chambliss, the vice chairman, speak to reporters about the NSA cull of phone records. Photograph: Alex Wong/Getty Images

Feinstein said she believed the order had been in place for some time. She said: "As far as I know this is the exact three-month renewal of what has been the case for the past seven years. This renewal is carried out by the [foreign intelligence surveillance] court under the business records section of the Patriot Act. Therefore it is lawful. It has been briefed to Congress."

The Center for Constitutional Rights said in a statement that the secret court order was unprecedented. "As far as we know this order from the Fisa court is the broadest surveillance order to ever have been issued: it requires no level of suspicion and applies to all Verizon [business services] subscribers anywhere in the US.

"The Patriot Act's incredibly broad surveillance provision purportedly authorizes an order of this sort, though its constitutionality is in question and several senators have complained about it."

Russell Tice, a retired National Security Agency intelligence analyst and whistleblower, said: "What is going on is much larger and more systemic than anything anyone has ever suspected or imagined."

Although an anonymous senior Obama administration official said that "on its face" the court order revealed by the Guardian did not authorise the government to listen in on people's phone calls, Tice now believes the NSA has constructed such a capability.

"I figured it would probably be about 2015" before the NSA had "the computer capacity … to collect all digital communications word for word," Tice said. "But I think I'm wrong. I think they have it right now."