WASHINGTON — The National Security Agency is collecting less than 30 percent of all US call records because of an inability to keep pace with the explosion in cellphone use, according to current and former federal officials.
The disclosure contradicts popular perceptions that the government is sweeping up virtually all domestic phone data. It is also likely to raise questions about the efficacy of a program that is premised on its breadth and depth, on collecting as close to a complete universe of data as possible in order to make sure that clues aren’t missed in counterterrorism investigations.
In 2006, the officials said, the NSA was collecting nearly all records about Americans’ phone calls from a number of US companies under a then-classified program, but as of last summer that share had plummeted to less than 30 percent.
The government is taking steps to restore the collection — which does not include the content of conversations — closer to previous levels. The NSA is preparing to seek court orders to compel wireless companies that currently do not hand over records to the government to do so, said the current and former officials, who spoke on condition of anonymity to discuss internal deliberations.
That effort comes after President Obama’s decision last month to find a way to move the data out of the government’s hands to assuage concerns about intrusions on privacy. Obama has given the Justice Department and the intelligence community until March 28 to come up with a plan.
The actual percentage of records gathered is somewhere between 20 and 30 percent, and reflects Americans’ increasing turn away from the use of land lines to cellphones, as well as technical challenges in preparing the NSA database to handle large amounts of new records, the current and former officials said.
That still likely represents tens of billions of records going back five years, a cause of great concern to privacy and civil liberties advocates.
In defending the program, administration officials have emphasized the need to gather all records. ‘‘If you’re looking for the needle in the haystack, you have to have the entire haystack to look through,’’ Deputy Attorney General James Cole told Congress last July.
Edward Felten, a Princeton University computer scientist who has studied the program from a technological perspective, said the revelation ‘‘calls into question whether the rationale offered for the program is consistent with the way the program has been operating.’’
But collection of even a quarter of the records is valuable, officials say.
‘‘It’s better than zero,’’ said Rick Ledgett, NSA deputy director, in an interview Thursday, without describing the program’s exact scope. ‘‘If it’s zero, there’s no chance.’’
One former senior official acknowledged that 100 percent was the goal, but asserted that as long as the collection ‘‘is fairly spread across the different vendors in the geographic area that you’re covering,’’ the collection provides value.
The NSA, for instance, is still able to obtain the call records of some customers whose phone companies are not covered by the program. When the customers of a non-covered carrier call customers of a covered carrier, the latter’s records should reflect both ends of the call.
Some industry officials said that the 20 to 30 percent figure can only be explained if the NSA is also missing records from companies that provide Internet-based calls.
‘It’s better than zero. If it’s zero, there’s no chance.’Rick Ledgett, NSA deputy director, on the percentage of data collected
According to industry and government figures, the number of land lines in use fell from 127 million in 2009 to 96 million in 2012, a 24 percent drop. By contrast, the number of cellphones in use in the United States jumped from 255 million in 2007 to 326 million in 2012, a 28 percent rise. And Internet-based subscribers, according to the Federal Communications Commission, shot up from 26 million in 2009 to 42 million in 2012, a 62 percent rise.
The NSA collection program began without court or congressional approval after the Sept. 11, 2001, attacks but was placed under court supervision in 2006 when US phone companies balked at providing the data solely at the request of the executive branch.
Under the program, the NSA receives daily transfers of call metadata from several of the nation’s largest phone companies.
Those records include numbers called, the calls’ time and duration, but not the content of conversations, subscriber names or cell tower location data.
The bulk collection began largely as a land-line program, focusing on carriers such as AT&T and Verizon Business Network Services.
At least two large wireless companies are not covered — Verizon Wireless and T-Mobile US, which was first reported by the Wall Street Journal.
Industry officials have speculated that partial foreign ownership has made the agency reluctant to issue orders to those carriers. But US officials said that was not a reason.