Like its predecessor, the Obama administration says it cannot count how many people in the U.S. have had their telephone calls and emails monitored by government agents in national security investigations under federal surveillance law.

The national intelligence office said in a letter this week to two Senate Democrats that it was "not reasonably possible to identify the number."

The senators, Ron Wyden of Oregon and Mark Udall of Colorado, worry that the government may be monitoring communications of law-abiding citizens with inadequate justification.

"We're not asking these questions to embarrass the administration or make the intelligence community's job more difficult," Wyden said in a statement Thursday. "Congress needs to know if the laws it writes are being interpreted and implemented as intended before it is asked to extend them, and failing to assure the public that government agencies aren't violating the rights of law-abiding Americans erodes public confidence and makes it harder for intelligence agencies to do their jobs."

The letter from the office of James Clapper, director of national intelligence, was a response to the senators' requests for information about how the Obama administration is interpreting amendments in 2008 to the Foreign Intelligence Surveillance Act. Wyden and Udall say they are concerned that the administration may be engaging in expansive interpretations of the 2008 law, which is scheduled to expire in late 2012.

The 2008 FISA amendments allow the government to obtain from a secret court broad, yearlong intercept orders that target foreign groups and people overseas, raising the prospect that phone calls and e-mails between those foreign targets and innocent Americans in this country will be swept in.

In saying it was unable to provide a number for those in the U.S. whose communications were collected, the administration's letter pointed Wyden and Udall to classified reports provided to Congress which give the number of circulated intelligence reports that refer to at least one person in the United States and give the number of collection targets later determined to be in the United States.

Wyden, however, said it was unacceptable that the administration was asserting it cannot give Congress "at least a ballpark estimate."

Jim Dempsey, a privacy expert and vice president of the Center for Democracy and Technology, an advocacy group that monitors Internet privacy, said the classified reports to Congress probably mention few people in this country because they deal only with those cases where surveillance was clearly justified.

"What is of concern are the people in the middle," Dempsey said. "These are innocent U.S. citizens and others in the U.S. whose communications were intercepted in the course of targeting non-U.S. persons overseas, but whose connection with terrorism is so non-existent that they don't even merit a mention in a disseminated report. Those people's communications are being listened to, and it is at least relevant to know how many people are in that bucket."

The administration's response was similar to the one the Bush administration gave in December 2007 when the White House Office of Management and Budget said that it would "likely be impossible" to count the number of people located in the United States whose communications were collected by the government.

"Is this still the case?" Wyden and Udall asked in a July 14 letter to Clapper, which elicited a response from Kathleen Turner, director of legislative affairs for the Office of the Director of National Intelligence.

Two months ago, Wyden and Udall raised similar objections to the congressional renewal of Patriot Act provisions that allow broad searches for records in national security investigations.

A newly released report by the American Civil Liberties Union said the public debate over reauthorization of the Patriot Act has been hampered by excessive secrecy. The search provision enables the government to obtain orders from the secret court to seize "any tangible thing" the government says is relevant to a terrorism or espionage probe.

In a Senate Intelligence Committee hearing Tuesday, Wyden asked National Security Agency general counsel Matthew Olsen whether the FISA Amendments Act of 2008 has been the subject of "significant secret legal interpretations."

"Let me say yes," Olsen replied. "And then let me add that the answer is that ... in the course of implementing those provisions, the government — and I was part of this effort — submits pleadings" to the court, which decides whether to authorize requests for surveillance. In the same vein, Wyden asked Olsen whether legal interpretations of the Patriot Act are being kept secret.

"It is certainly fair to say that there are opinions from the court that are classified," Olsen replied. He said that those opinions have been provided to the Senate Intelligence Committee and that activities undertaken in accordance with those orders are subject to "extensive oversight from across the government."