Washington, Jun 11 (IANS): As US counter-intelligence agents have begun a probe into how information about secret government surveillance programmes was leaked, a new survey shows that more than half of Americans are fine with one of them.

Fifty-six percent consider the government's tracking of phone records an "acceptable way" to investigate terrorism, according to the new national survey released Monday by the Pew Research Centre and the Washington Post.

However, Americans are less supportive of the government's ability to monitor emails with 45 percent saying "yes", while 52 percent saying "no" to it, according to the survey.

These numbers are relatively unchanged from a similar question asked in July 2002, less than a year after the September 11 terrorist attacks in the US.

The survey was conducted Thursday through Sunday, as information about the federal surveillance programmes was being published by the Guardian and the Washington Post.

According to the Post, counterintelligence investigators are scrutinising how 29-year-old contractor Edward J. Snowden, who said he leaked "top-secret" National Security Agency documents, was able to gain access to what should be highly compartmentalised information.

The White House Monday welcomed a debate over the electronic surveillance programmes exposed by Snowden.

The Obama administration officials and leaders of the intelligence committees in Congress said the programme undergoes periodic review by all three branches of government, and that the content of Americans' calls is not being monitored.

White House spokesperson Jay Carney Monday said the measures are a necessary middle way between total privacy and unacceptable threat.

He said President Barack Obama would be willing to consider changes should a national debate show the public wants them, but noted "this is not the manner by which he hoped to have the debate".

Republican Peter King, chairman of the House Homeland Security Committee's Subcommittee on Counterterrorism and Intelligence, called Snowden "a defector" who should be turned over to the US with an eye toward harsh prosecution.

"This person is dangerous to the country," King told CNN Monday.