Obama on defensive as senators irate over NSA's PRISM tapping

On the eve of a major US Senate hearing on the National Security Agency's bulk surveillance, two senators called for major reforms of the NSA's collection of phone records and accused US intelligence leaders of misleading the public about its impact on privacy.

US President Barack Obama's national security team on Wednesday acknowledged for the first time that when investigating one suspected terrorist, it can read and store the phone records of millions of Americans.

Since it was revealed recently that the National Security Agency puts the phone records of every American into a database, the Obama administration has assured the nation that such records are rarely searched and, when they are, officials target only suspected international terrorists.

A letter sent by the director of national intelligence, James Clapper, to Ron Wyden, a Democratic senator for Oregon, on Friday said that there had been "a number of compliance problems" with the NSA's bulk, ongoing collection of millions of Americans' phone records, but "no findings of any intentional or bad-faith violations".

On the Senate floor late on Tuesday afternoon, Wyden, a member of the Senate intelligence committee, all but accused Clapper of lying.

Any policymaker who simply defers to intelligence officials without asking to see their evidence is making a mistake," Wyden warned.

Clapper has already apologised for untruthfully testifying during a March Senate colloquy with Wyden that the NSA does "not wittingly" collect data on millions of Americans. Representatives for Clapper did not immediately return a request for comment on Wyden's accusation (Sere: Top US officials questioned over NSA surveillance programmes) .

Meanwhile, at a hacker convention in Las Vegas on Wednesday, the head of the NSA said government methods used to collect telephone and email data helped foil 54 terror plots - a figure that drew open scepticism from lawmakers back in Washington.

"Not by any stretch can you get 54 terrorist plots," said the chairman of the Senate Judiciary Committee, Sen Patrick Leahy.

More than a decade after the terror attacks of 2001, the phone-record surveillance programme has stirred deep privacy concerns on Capitol Hill, where Leahy said Wednesday during an oversight hearing: "If this program is not effective, it has to end," adding that, "So far I'm not convinced by what I've seen."