U.S. President George Bush has announced that he will be vetoing a bill that would ban the CIA from using harsh interrogation methods such as waterboarding.

Bush said in his weekly radio address on Saturday that the legislation would take away "one of the most valuable tools in the war on terror."

Jennifer Daskal, senior counterterrorism counsel at Human Rights Watch, told The Associated Press that Bush "will go down in history as the torture president" for defying Congress.

"The Bush administration continues to insist that CIA and other non-military interrogators are not bound by the military rules and has reportedly given CIA interrogators the green light to use a range of so-called enhanced interrogation techniques, including prolonged sleep deprivation, painful stress positions, and exposure to extreme cold," Daskal said.

The bill passed through the House of Representatives and the Senate in February. It was to set new guidelines for intelligence gathering, including limits on interrogation techniques.

Its supporters say that the bill will help the U.S. regain its moral authority in the international playing field. The U.S. military is currently banned from using such techniques.

Both Sens. Barack Obama and Hillary Clinton, who are running for the Democratic presidential nomination are in favour of the torture ban. Sen. John McCain, the presumed Republican presidential candidate, says that waterboarding is torture but is not supporting the bill.

"I believe that waterboarding is torture and in violation of many laws including the Geneva Convention," McCain said at a campaign rally in February. "I don't believe that the army field manual should be the only document that the CIA should be restricted to but that the CIA should also should be restricted from using any techniques that constitute cruel, inhumane or degrading treatment."

Waterboarding is a technique that simulates drowning. The subject lies on their back with their head tilted downwards as water is poured over their face and into their breathing passages.

"The person believes they are being killed, and as such, it really amounts to a mock execution, which is illegal under international law," John Sifton of Human Rights Watch has said. 

But Bush says now is not the "time for Congress to abandon practices that have a proven track record of keeping America safe."

Torture doesn't work: critics

The situation is murky because there is so little on the public record that would support or not support Bush's assertions.

"I have heard nothing to suggest that information obtained from enhanced interrogation techniques has prevented an imminent terrorist attack," Democratic Senator Jay Rockefeller, chairman of the Senate intelligence committee said.

Critics say that torture does not produce truthful confessions and say that unlike the Fox television show "24," there is almost never a "ticking clock" situation.

"24" has come under criticism because in the show, intelligence agent Jack Bauer is constantly torturing terrorists to get vital information out of them, as a clock ticks down on some national threat.

Bush asserts that waterboarding and other torture methods have been used successfully, but for security reasons, the CIA cannot release its successes.

The army field manual restricts its members from using torture for intelligence gathering.

House speaker Nancy Pelosi says that she will work to override Bush's veto nest week, but the odds are stacked against her.

Based on the margin of passage in each chamber, it will be difficult for the Democratic-controlled Congress to turn back Bush's veto. It takes a two-thirds majority, and the House vote was 222-199 and the Senate's was 51-45.

CIA director Michael Hayden pledged that whatever the result, the "CIA will continue to operate within the law."

With files from The Associated Press