A White House-appointed panel on Wednesday proposed curbs on some key National Security Agency surveillance operations, recommending limits on a program to collect records of billions of telephone calls and new tests before Washington spies on foreign leaders.

Among the panel's proposals, made in the wake of revelations by former NSA contractor Edward Snowden, the most contentious may be its recommendation that the eavesdropping agency halt bulk collection of the phone call records, known as "metadata."

Instead, it said, those records should be held by telecommunications providers or a private third party. The US government would need an order from the Foreign Intelligence Surveillance Court for each search of the data.

"We don't see the need for the government to be retaining that data," said Richard Clarke, a member of the panel and a former White House counterterrorism adviser.

The panel's report expressed deep skepticism about both the value and effectiveness of the metadata collection program.

"The question is not whether granting the government (this) authority makes us incrementally safer, but whether the additional safety is worth the sacrifice in terms of individual privacy, personal liberty and public trust," it said.

The report's authors said the metadata collection program "has made only a modest contribution to the nation's security." The program "has generated relevant information in only a small number of cases" that might have led to the prevention of terrorist attack, they said in a footnote.

It added that "there has been no instance in which NSA could say with confidence that the outcome would have been different without the ... telephony metadata program. Moreover, now that the existence of the program has been disclosed publicly, we suspect that it is likely to be less useful still."

It remains to be seen, however, how many of the panel's 46 recommendations will be accepted by US President Barack Obama and the US Congress. The panel's five members met with Obama at the White House on Wednesday.

Obama said in a television interview this month that he would be "proposing some self-restraint on the NSA" in reforms that the White House has said will be announced in January.

White House press secretary Jay Carney said some of the outside panel's recommendations could be accepted, others studied further, and some rejected.

Reuters