Mr Bush says Mr Bolton is the right man for the job

Mr Bush said Mr Bolton was the "right man at the right time" for the job.

On Tuesday, senators delayed a vote on the nomination until next month to examine new allegations.

Mr Bolton - a well-known critic of the UN - is accused of poor management and influencing intelligence, but the White House says the charges are unfounded.

He also has the backing of Secretary of State Condoleezza Rice.

The Senate delayed the vote after Republican Senator George Voinovich indicated he would side with the Democrats, who oppose Mr Bolton's nomination.

At least two other Republicans, Lincoln Chafee and Chuck Hagel, are now voicing doubts about Mr Bolton's temperament and credibility.

'Damaged goods'

The New York Times newspaper quoted Christopher Dodd, a Democrat on the committee, as saying he hoped the administration would now abandon the nomination.

John's distinguished career and service to our nation demonstrate that he is the right man at the right time for this important assignment George W Bush

"My hope would be that the administration, after yesterday, would say that he's damaged goods," he said.

"You'd think at some point, they'd wait a few days or whatever and decide this nomination isn't worth it to have a one-vote victory."

But Mr Bush, in a speech to insurance brokers about social security proposals, made it clear he would not give up on his nominee.

"John's distinguished career and service to our nation demonstrate that he is the right man at the right time for this important assignment," he said.

Democrats are now seeking to investigate allegations that Mr Bolton tried to have a CIA analyst removed from his job.

They have asked to interview several senior intelligence officials, including former deputy CIA director John McLaughlin, AP news agency said quoting a unnamed committee member of staff.