The surprise turn of events occurred after a number of Democrats complained that the Republican-led committee was forcing a vote on the nomination without considering new allegations against Mr. Bolton.
Democrats are concerned about allegations that Mr. Bolton, currently undersecretary of state for arms control and international security, sought the removal of an analyst who disagreed with his assessment that Cuba possessed banned weapons. They also believe his outspoken criticism of the United Nations, he has called the world body corrupt and irrelevant, makes him unsuitable for the job.
But Democrats say they have uncovered new allegations against Mr. Bolton since his confirmation hearing last week, and they were furious that committee chairman Senator Richard Lugar had denied their request for additional hearings into the matter.
“It seemed extraordinary that you would not give us another week,” said Senator Barbara Boxer of California.
Senator Lugar was pressing for a vote Tuesday afternoon, apparently confident he had the votes in the Republican-led committee to send the nomination to the full Senate.
But then Republican Senator George Voinovich of Ohio took everyone by surprise.
“I have heard enough today that I do not feel comfortable voting for Mr. Bolton,” he said. “I think one's interpersonal skills and their relationship with their fellow man is a very important ingredient in anyone who works for me.”
With 10 Republicans and eight Democrats on the panel, Mr. Voinovich's vote against the nomination would have blocked it from going to the full Senate.
Senator Lugar, seeking to avoid defeat of the nomination, agreed to put off the vote until after a congressional recess next month, and left open the door to recalling the nominee.
“I would include the possibility that Secretary Bolton might be asked to come back for additional testimony,” said Mr. Lugar.
Mr. Lugar also put the State Department and the Central Intelligence Agency on notice that other witnesses may be asked to come before the committee to testify about the nominee.