The Obama administration’s top national security lawyers Monday rejected the idea that the government should stop collecting copies of every American’s telephone records every day, telling an independent oversight board that it would lose valuable time if each time it launched a terror investigation it had to seek the private billing records from individual phone companies.

The lawyers also told the Privacy and Civil Liberties Oversight Board during a rare public hearing that a secret overseas Internet data-gathering program exposed last week was not an attempt to evade scrutiny by the federal intelligence court that supervises such operations. Top officials of Google and Yahoo criticized the program, in which the National Security Agency reportedly tapped into fiber optic cables that funnel the data overseas. The government did not dispute that it tapped the cables overseas for Internet traffic but said it wasn’t doing so to avoid U.S. legal restrictions.

Much of the board’s session Monday with government lawyers dealt with congressional proposals that would shift retention of phone and Internet records to private companies, instead of storing them at the National Security Agency. The lawyers warned that the government’s ability to conduct counter-terrorism investigations would be hampered by the loss of its massive data collections.

If Congress were to shut down the government’s collection of phone records, which it has been secretly doing since 2006, “we wouldn’t be able to see the patterns that the NSA’s programs provide us,” said Patrick Kelley, acting general counsel of the FBI. Kelley added that the FBI would not be able to weed out significant phone data if it did not have the NSA’s massive data bank to tap into, and would lose valuable time if it had to instead seek the data from individual phone companies.

Robert Litt, general counsel for the Office of the Director of National Intelligence, said the White House is considering keeping copies of the records for fewer than five years and may reduce the types of information that it searches. But Litt and other government attorneys did not elaborate on these possibilities or offer detailed critiques of the congressional proposals they said they opposed.

The NSA’s general counsel, Rajesh De, declined to discuss published accounts describing the U.S. tapping into fiber optic cables to extract Internet data about customers of Google and Yahoo without the knowledge of the technology companies. But De insisted that the program was not an attempt to avoid the supervision of the Federal Intelligence Surveillance Court.

“That is simply inaccurate,” De said. He said news accounts about the program contained inaccuracies but didn’t say what they were.

Eric Schmidt, Google’s chairman, told CNN he was shocked by the latest revelations. Schmidt described the operation as “perhaps a violation of law but certainly a violation of mission.” He added that it was “clearly an overstep.” Schmidt once famously told an interviewer, “If you have something that you don’t want anyone to know, maybe you shouldn’t be doing it in the first place.”

In a blog posting Monday, the Washington Post said it did not know the exact details of how the NSA and its British counterpart, GCHQ, intercept and then tap into Internet data funneling through fiber optic cables routing information for Google and Yahoo. But the newspaper published a series of internal NSA slides that appeared to show elements of agency programs and techniques that could be used to extract consumer information as it flows across the cables.

The slides were provided to the newspaper by former NSA contract employee Edward Snowden, who is being sought by the U.S. for leaking classified information. Some of the slides, which show how the material is routed, were analyzed by technology experts, who helped explain how the information was intercepted.

The five members of the Privacy and Civil Liberties Oversight Board are appointed by President Barack Obama but report to Congress. The board has set no deadline but has been meeting for months with national security officials to scrutinize the surveillance programs and their impact on civil liberties.

Two board officials said last week that the panel hoped to deliver its report to Obama and Congress by the end of the year.

The officials, speaking on condition of anonymity because they were not authorized to reveal the board’s plans, said the board intends to present the bulk of its report directly to Obama and Congress, without any advance scrutiny. Because the oversight board reports to Congress, it is not subject to the supervision of the White House and the Director of National Intelligence, which oversees a similar effort by a separate presidentially-appointed advisory panel, the Review Group on Intelligence and Communications Technologies.