GEORGE BUSH'S decision to bypass court review and authorise domestic wiretapping by executive order is part of an effort to rebuild presidential powers weakened in the 1970s as a result of the Watergate scandal and the Vietnam War, the US Vice-President, Dick Cheney said.

Mr Cheney, who cut short a trip that included the Middle East and Pakistan, said threats facing the country require that the President's authority under the constitution be "unimpaired".

"Watergate and a lot of the things around Watergate and Vietnam … served to erode the authority I think the President needs to be effective, especially in the national security area," Mr Cheney said on Tuesday as he flew back to Washington to support Mr Bush.

His remarks came after US District Judge James Robertson, one of 11 members of the secret Foreign Intelligence Surveillance Court, resigned in protest at Mr Bush's secret authorisation of the domestic spying program, sources told The Washington Post. Judge Robertson sent a letter to the Chief Justice, John Roberts, on Monday notifying him of his resignation.

Associates said Judge Robertson had privately expressed deep concern that the warrantless surveillance program was legally questionable and may have tainted the Foreign Intelligence Surveillance Court's work.

Mr Cheney, however, dismissed the idea that Americans were concerned about a potential abuse of power, saying that any backlash was likely to punish the President's critics, not Mr Bush.

"The President and I believe very deeply that there is a hell of a threat," Mr Cheney said, calculating that "the vast majority" of Americans support the Administration's surveillance policies. "And so if there's a backlash pending, I think the backlash is going to be against those who are suggesting somehow we shouldn't take these steps in order to defend the country."

On Capitol Hill, calls for a congressional investigation escalated, with a group of Democrats and Republicans on the Senate intelligence committee asking to join hearings already scheduled by the Senate judiciary committee.

Barbara Boxer, a Democrat, said she had written to several constitutional scholars to ask whether Mr Bush committed an impeachable offence by ordering the National Security Agency in 2002 to engage in warrantless surveillance within the US.

Osama bin Laden may no longer be able to run al-Qaeda and has not been heard from for nearly a year, the US Defence Secretary, Donald Rumsfeld, said yesterday.

Mr Rumsfeld, who was visiting Pakistan a day after Mr Cheney's trip, said: "I think it is interesting that we haven't heard from [bin Laden] for close to a year.

"I don't know what it means, but I suspect … if he is alive and functioning, that he is spending a major fraction of his time trying to avoid being caught."