WASHINGTON - Unexpected cracks in Republican support threw into limbo President Bush's high-profile nomination of John R. Bolton to be the country's representative at the United Nations.

The postponement Tuesday of a Senate committee vote on Bolton was a political defeat for Bush - at least in the short term - and opened the possibility that the nomination could fall.

The White House late Tuesday continued to express full support for the nomination, which hit a snag earlier in the day when a few Republicans on the Senate Foreign Relations Committee joined Democrats in asking to delay a vote in favor of a fresh look at allegations of unbecoming conduct.

Both Democrats and Republicans had predicted earlier the GOP-controlled committee would vote along party lines to recommend Bolton for the job.

"The dynamic has changed," said Sen. Lincoln Chafee, R-R.I. "A lot of reservations surfaced today. It's a new day."

The committee set no new date for a vote, but a delay of at least two weeks seemed likely. Democrats planned to use the time to investigate new allegations that Bolton abused his authority and mistreated subordinates, and to look into Bolton's unusual request for the names of other U.S. officials whose communications were secretly picked up by a U.S. spy agency.

Among the new allegations were those of a Dallas businesswoman who said Bolton grew irrationally angry over a business dispute, chased her through a hotel and threw things at her at an international conference a decade ago. Bolton was "genuinely behaving like a madman," Melody Townsel, a former U.S. Agency for International Development worker, wrote in a letter to the committee read aloud at Tuesday's hearing by Sen. Joseph Biden, D-Del.

At the White House, press secretary Scott McClellan called allegations of abusive personal behavior unfounded and said Bush stood by the nomination unequivocally.

"John Bolton is exactly the person we need at the United Nations at this time," McClellan said.

There was no indication Tuesday that Bolton might withdraw his name, but it was clear his nomination was in some trouble.

"My own hope is that the president decides to nominate someone else for this important position of U.N. ambassador," Sen. Barbara Boxer, D-Calif., said after Tuesday's tense committee meeting. "Surely there must be many other men and women who could fulfill this post with honor."

The decision to postpone a vote closed a rancorous session in which some Democrats bluntly questioned Bolton's veracity and repeatedly appealed for more time to investigate.

Republicans hold a 10-8 majority on the panel, and Lugar had sounded confident early in the session that he had the votes to prevail. He pushed hard for an immediate vote, over loud objection from Democrats.

The tide turned when Ohio Republican Sen. George Voinovich spoke for the first time. He did not attend Bolton's two-day confirmation hearing last week but had been presumed to be a supporter.

"I don't feel comfortable voting today," Voinovich said.

Chafee and fellow Republican Sen. Chuck Hagel of Nebraska also expressed reservations about a quick vote, and Hagel warned that he may not support Bolton's nomination if it moves to the full Senate for a confirmation vote.

"What's happening is that some Democrats on the committee are continuing to raise unfounded allegations," McClellan said. "We believe John Bolton has addressed all these issues. He's testified for more than eight hours. He's responded to many questions in writing as well, and we look forward to addressing any questions the committee members continue to have."

Bolton, 56, is the State Department's arms control chief. He would replace John Danforth as U.N. ambassador.

Much of Bolton's two-day confirmation hearing last week focused on claims that he retaliated against lower-level State Department employees who disagreed with him.

Since then, Democrats have uncovered other allegations about Bolton's personal dealings. Biden, the senior Democrat on the panel, said they have found instances in which Bolton's Senate testimony doesn't seem to match the facts.

After Tuesday's committee meeting, Voinovich told reporters he had planned to support Bolton but changed his mind after an impassioned critique from Sen. Christopher Dodd, D-Conn. Voinovich said he did not fear retribution from the White House, which had counted on solid Republican support.

"The passion on the other side on this, I don't think is political," Voinovich said. "I think they raised some legitimate issues. I think we ought to find out what they are, I think we ought to get the information, get a chance to have (the allegations) rebutted."

Bolton may be asked to return for more testimony, and the committee may also now call additional witnesses, Democrats said afterward.