For all the attention generated by the controversy over Edward Snowden's disclosures of US spying operations, much of the American public has paid little attention to the details of the policy debate over government surveillance, polls show.

The latest evidence comes from a new Pew Research Center poll showing that half the US public said they had heard nothing at all about President Barack Obama's speech Friday outlining new restrictions on the National Security Agency.

Only eight per cent of those surveyed said they had "heard a lot" about Obama's plans.

Of those who said they had heard at least a little bit about the speech, the overwhelming majority said they thought the president's plans would have little impact either on protecting privacy or on hindering the government's fight against potential terrorist plots.

About one in five said Obama's plans would increase the protection of individual privacy and about one in eight said it would make fighting terrorism more difficult.

The poll echoed other surveys in showing that the public has grown more disapproving of the NSA's surveillance programme.

By 53 per cent to 40 per cent, Americans said they disapproved of "the government's collection of telephone and internet data as part of anti-terrorism efforts".

In July, a Pew poll showed the public approving of the programmes by a narrow margin. By 48 per cent to 41 per cent, the public said that current limits on what the government collects were not adequate.

Democrats were more inclined than Republicans to say they approved of the NSA's efforts.

Republicans who said they considered themselves tea party supporters were particularly negative, disapproving of NSA surveillance by 68 per cent to 27 per cent.

That division likely reflected the fact that on virtually all measures, partisans tended to trust government more when their party controlled it.

Another significant division on the question involves age: Americans younger than 30 were particularly likely to disapprove of what the NSA did.

Asked about Snowden, Americans offered somewhat contradictory opinions. The public was almost equally divided on the question of whether Snowden has served or harmed the public interest, with Americans younger than 30 significantly more inclined to see his actions positively while those over 65 see them negatively.

By 56 per cent to 32 per cent, Americans said they thought the government should pursue a criminal case against Snowden.

Those under 30 divided evenly on the question, while all other age groups supported prosecution by large margins.

Even those who said they disapproved of the NSA's surveillance programmes split evenly on the question of whether Snowden should be prosecuted for revealing them.

- MCT