Bolton has proved a controversial choice

A US Senate committee delayed the vote by one week, in line with wishes of Democrats on the panel, who strongly oppose the nomination.

A former senior US official Carl Ford has said Mr Bolton is a bully who is unsuitable for the job.

But Secretary of State Condoleezza Rice has praised Mr Bolton.

Democrats building case

On Wednesday, she heralded his management style, and said Mr Bolton - who is strong critic of the UN - would be a strong proponent for change at the organisation.

When asked by correspondents whether accusations that he was a serial abuser stood up, she said: "It's certainly not the John Bolton that I know or that a lot of other people know.

"John Bolton has been a very effective manager, diplomat.

JOHN BOLTON Yale Law School graduate As assistant secretary of state under George Bush senior, helped organise anti-Saddam alliance Made under-secretary of state for arms control and international security in May 2001 In July 2003, condemned North Korean leader Kim Jong-il for living like royalty while people lived in "hellish nightmare" Profile: John Bolton

"He has a lot of people who have worked for him, who are loyal to him and where he has brought out the best in his people," she added.

A party-line vote is likely to take place on the nomination, and as the Senate is Republican-controlled, Mr Bolton will almost certainly be approved.

Democrats are seeking classified documents relating to complaints that Mr Bolton attempted to make intelligence analysts alter their reports to reflect a speech he was giving.

"We still don't have answers back from the State Department on some papers," said Senator Joseph Biden of Delaware, a key Democrat on the committee.

At Tuesday's hearing, Carl Ford, who ran the State Department's Bureau of Intelligence and Research, said Mr Bolton was a serial abuser of junior staff.

He said his treatment of an intelligence analyst who disagreed with him on the subject of Cuba damaged the work of the department.

Mr Bolton is a "kiss up, kick down" bureaucrat, he said.