WASHINGTON (AFP) - US President Barack Obama welcomes a debate about the tradeoff between civil liberties and security, his spokesman said Thursday amid a furor over government hoarding of domestic telephone records.

But despite the sensitivity of constitutional and legal questions around the issue, Mr Obama remains determined to use all tools to keep the United States safe from terrorism, spokesman Josh Earnest said on Air Force One.

"The president welcomes the discussion of the tradeoff between security and civil liberties," Mr Earnest said, while refusing to comment directly on a phone records data mining program disclosed by the Guardian newspaper.

"The top priority of the president of the United States is the national security of the United States. We need to make sure we have the tools we need to confront the threat posed by terrorists.

"What we need to do, is balance that priority with the need to protect civil liberties."

Mr Earnest argued that secret surveillance activities being conducted by US spy agencies were subject to "robust" oversight by Congress and the courts and that Mr Obama had strengthened the safeguards since taking office.

But he said Mr Obama understood why some people could look at reports of the programme and believe the correct balance had not been struck.

He also reiterated that a secret court order published by the Guardian does not allow the US government to listen in on calls made by Americans nor does it call for phone companies to turn over the names of those making calls.

It instead requires phone companies to hand over telephone numbers, data on the length of conversations and other details, Mr Earnest said.