WASHINGTON -- A Senate panel delayed a crucial vote yesterday on President Bush's nomination of John Bolton to be the United States' ambassador to the United Nations after a Republican senator stunned the Foreign Relations Committee by saying he would oppose the nomination if forced to take a stand.

The delay exposes Bolton, a controversial State Department hawk, to at least three more weeks of efforts by Democrats to derail his nomination as other Republicans waver over allegations that Bolton intimidated subordinates over disagreements about policy and intelligence assessments.

The delay also marks a setback for the Bush administration, which was trying to push the nomination through the committee in the face of the wavering support of two moderate Republicans, Sens. Lincoln Chafee of Rhode Island and Chuck Hagel of Nebraska.

But it was a third Republican, Sen. George Voinovich of Ohio, who voiced doubts about Bolton yesterday and forced a delay in the vote.

"I've heard enough today that I don't feel comfortable about voting for Mr. Bolton," Voinovich said. "I've heard enough today that gives me concern as a member of this committee."

There are 10 Republicans and eight Democrats on the committee. If Voinovich voted against Bolton, it would have created a 9-9 tie, blocking the nomination from going to the full Senate.

"If the votes play out the way I suspect they will play out if we push this vote, the Bolton nomination will not come out of this committee," Hagel said.

The delay, a victory for Senate Democrats, also was the latest in signs that Republican moderates in Congress are beginning to bridle at their party leadership's strong tilt to the right and insistence on party discipline.

Yesterday's delay came despite attempts by Lugar to muscle a vote through the committee. Over Democratic protests, Lugar cut off senators who wanted to continue debating and offering motions, apparently thinking he had the votes to pass the nomination.

"We have indulged, I believe, in a lot of give," Lugar said at one point. "So, the give is over."

But after Voinovich voiced reservations, Lugar invited Democrats to offer a motion to delay the vote while aides to both sides interviewed additional witnesses and compiled information about Bolton's background.

Bolton was accused during last week's confirmation hearing of seeking to have at least two intelligence analysts removed from their jobs for disagreeing with him. One witness, a former State Department intelligence chief, testified that Bolton was a "serial abuser," but committee Republicans said the episodes were "isolated incidents."

Since then, at least one other intelligence analyst said he was threatened by Bolton, and other former co-workers have provided information about confrontations.

Voinovich, who missed last week's confirmation hearing, said the allegations troubled him. "I think one's interpersonal skills and their relations with their fellow man is a very important ingredient for anyone who works for me," Voinovich said.

Moderate congressional Republicans have showed signs of unease at the tough stance taken by GOP leaders and the Bush administration. On another issue, Rep. Christopher Shays, a Republican from Connecticut, recently broke ranks and called for House Majority Leader Tom DeLay, a Republican from Texas, to step down from his leadership post in the face of questions about the ethics of his fundraising, foreign travel and relationships with lobbyists.