Judge Michael Mukasey, the nominee for US attorney-general, on Wednesday distanced himself from the White House policy on torturing terrorism suspects, and promised to resign if the president acted unconstitutionally.

Testifying at his Senate confirmation hearings, Mr Mukasey reassured Democrats he would remain independent of the White House, even in matters of national security.

Alberto Gonzales, the former attorney-general, has been widely criticised for allowing his close political relationship with the White House to trump his commitment to the rule of law.

Mr Mukasey criticised a 2002 justice department document, the so-called Bybee memo, that said George W. Bush had the power to issue orders that violated US or international laws prohibiting torture. That memo, which was later withdrawn by the government, was “worse than a sin, it was a mistake. It was unnecessary”, Mr Mukasey said.

He criticised the administration’s policy on indefinite detention of terrorism suspects. The Supreme Court ruled such detentions were legal, he said, “but that’s not to say that, as a matter of policy, it’s a wise thing to do, that it doesn’t hurt us with allies on whom we rely for support in fighting the people we have to fight”.

He promised to do more to protect US civil liberties in the war on terror but left open the possibility he would not oppose the warrantless surveillance of US citizens, saying he could not make a decision on the legality of the secret eavesdropping programme until he knew the details.

Congress and the Bush administration are locked in a dispute over legislation that would permit the Na­tional Security Agency to intercept the communications of suspected terrorists, including Americans with suspected links to terrorism.

Republican lawmakers on Wednesday night forced Democrats to put off a vote on the legislation.

House of Representatives Democratic leaders pulled the bill from consideration after Republicans threatened a procedural move that could have forced bill supporters to cast a vote seeming to side with al-Qaeda leader Osama bin Laden.

The White House has threatened to veto the measure on grounds it contains unnecessary restrictions that would hamper the ability of the intelligence community to collect intelligence. One area of dispute is whether the legislation should provide companies that have helped the government with eavesdropping programmes with retrospective immunity.

The big telecommunications companies have found themselves in the uncomfortable position of being pressed by congressional investigators for information about the wiretapping programme while being told by security and administration officials they cannot even acknowledge its existence.

“Our company essentially finds itself caught in the middle of an oversight dispute between the Congress and the executive relating to government surveillance activities,” Wayne Watts, general counsel for AT&T, the largest US telecommunications group, wrote to the House energy and commerce committee.