Correction: A previous version of this story incorrectly attributed a quote to Sen. Mark Udall (D-Colo.) His cousin, Sen. Tom Udall, actually said, “It’s very, very difficult to have a transparent debate about secret programs based on secret orders from a secret court.” This version has been corrected.

Members of Congress and The White House are defending a top secret NSA program that continues to collect data from millions of phone records, but civil liberties supporters remain skeptical. The Post’s Ellen Nakashima explains. (The Fold/The Washington Post)

A small group of lawmakers who have consistently but obliquely warned about the collection of Americans’ telephone data remains troubled by other aspects of the government’s surveillance programs that remain secret.

And, following the leak of classified records in recent days, they are pressing the administration to release information on the legal rationales for its sweeping collection powers and how it is using any stored data obtained from Americans as part of its counterterrorism efforts.

“So, here I have my Verizon phone, my cellphone, what authorized investigation gave you the grounds for acquiring my cellphone data?” said Sen. Jeff Merkley (D-Ore.), waving his phone in front of Gen. Keith B. Alexander when the director of the National Security Agency appeared before the Senate on Wednesday.

The leak of a highly classified court order showed that Verizon Business Network Services was turning over all domestic call records and that the government is collecting data on tens of millions of Americans — a situation that an ideologically diverse group of Senate and House lawmakers had long been hinting at.

Demanding public answers to questions they have posed for years, these lawmakers say the administration has not yet provided the level of disclosure Americans deserve.

Merkley, for instance, was referring to the fact that the law under which the phone records are obtained requires reasonable grounds to believe the records sought are “relevant to an authorized investigation . . . to protect against international terrorism.”

How could there be one authorized investigation that enables the collection of “all phone records, all the time, all locations?” Merkley asked. How, he continued, “has the standard of the law been met?”

Some experts believe the government has created a secret umbrella investigation that has facilitated the crafting of court orders to cover all phone records. But the existence of any such investigation and related legal opinions and court orders remains classified.

Alexander declined to discuss specifics, deferring to the Justice Department on the classification question. But he said he thought the government should see “if we can get it declassified and out to the American people so they see exactly how we do it.”

The surveillance programs are authorized by the USA Patriot Act, a law passed after the Sept. 11, 2001, attacks. Just over two years ago, when the measure came up for reauthorization, some senators said the administration’s secret interpretation of the law was allowing it to sweep up large amounts of data about the communications of Americans.

“When the American people find out . . . they are going to be stunned and they are going to be angry,” Sen. Ron Wyden (D-Ore.) said on the Senate floor in May 2011.

“Millions of innocent citizens are having their records looked at,” Sen. Rand Paul (R-Ky.) said the same month. On Thursday, Paul said he plans to bring legal action against the government over its surveillance efforts.

Recent revelations have provided details about their previously veiled alarm. And the disclosures have refocused attention on equally cryptic warnings about other government surveillance programs involving the collection of e-mail and other Internet data and what critics contend is a “backdoor search loophole” to look through the communications of Americans without a warrant.

“It’s very, very difficult to have a transparent debate about secret programs based on secret orders from a secret court,” said Sen. Tom Udall (D-N.M.), expressing a long-standing frustration Wednesday during the hearing in which Alexander appeared before the Senate Appropriations Committee.

Tom Udall’s cousin, Sen. Mark Udall (D-Colo.), and Wyden, both members of the Intelligence Committee and briefed on the country’s mostly closely held secrets, have pressed for more transparency on how the Foreign Intelligence Surveillance Act (FISA) is interpreted and carried out. The phone records program, first disclosed by USA Today in 2006, is conducted under an amendment to the FISA law known as Section 215 — or the “business records provision” — of the Patriot Act.

The senators are also concerned about another FISA program, this one authorized by Section 702 of the 2008 FISA Amendments Act. That provision allows the government to collect the communication of foreign targets overseas through U.S. Internet firms, but it also means that Americans who communicate with the targets also have their e-mail picked up.

For the small part of the public that has closely followed Senate debates and the questioning of intelligence officials, the serial suggestions of government overreach have been tantalizing but also aggravating.

Gregory T. Nojeim, senior counsel at the Center for Democracy and Technology, said advocates have long realized that Wyden, Udall and others were sounding an alarm but could only guess at the specifics.

“They’ve been jousting with shadows,” Nojeim said.

Lawmakers from the right and the left have questioned the government’s exercise of its powers, including Sen. Bernard Sanders (I-Vt.), Sen. Richard J. Durbin (D-Ill.), Sen. Mike Lee (R-Utah), Rep. Jerrold Nadler (D-N.Y.) and Rep. John Conyers Jr. (D-Mich.).

Their concerns go back to the fraught days following the Sept. 11 attacks when Congress, under pressure to prevent further attacks, passed the Patriot Act. One provision was Section 215, which made it easier for authorities to obtain the records of Americans.

Before 2001, the records were linked to travel: They could be from hotels, rental car agencies, airlines. And they had to be relevant to a particular person — an “agent of a foreign power.”

With 215’s passage, the government could now get “any tangible things” — not just hotel records, but phone records and library records. And, significantly, they did not have to belong to a suspected terrorist or spy. They only had to be relevant to an authorized investigation.

“That was the big change,” Nojeim said. “You’re taking away the provision that protects Americans. Bam. Now you’ve got the records of everyone.”