WASHINGTON -The president’s nominee to be America’s ambassador to the United Nations, John Bolton, suffered a major setback yesterday when a Republican senator shocked the Senate Foreign Relations Committee by saying that at this point, he would not vote to approve him.

“I’ve heard enough today that I don’t feel comfortable voting for John Bolton,” said Senator Voinovich, a Republican from Ohio who had not attended the two previous hearings on the nomination. His comments forced the committee to delay the vote until next month.

Only minutes before Mr. Voinovich’s statement, the Republican chairman of the committee, Senator Lugar of Indiana, requested a roll call vote. But after Mr. Voinovich voiced his concerns, Mr. Lugar settled for a delay pushed by the committee’s Democrats, which he initially opposed.

“The reality was that a nine-to-nine vote would have killed the nomination,” Senator Allen, a Republican from Virginia, told reporters after the meeting.

In addition to Mr. Voinovich, Senators Chafee and Hagel, Republicans from Rhode Island and Nebraska, have in the last week indicated that their support for Mr. Bolton was wavering. Yesterday, Mr. Hagel said he would vote for Mr. Bolton in the committee but may not support him on the floor of the Senate. Mr. Chafee after the hearing said Republican support for Mr. Bolton was eroding.

The delay in the vote represents a victory for Democrats who have tried to paint Mr. Bolton as a serial abuser of staff who punished underlings if they disagreed with his ideologically driven intelligence assessment. So determined were Democrats to delay the vote yesterday that they invoked an obscure parliamentary rule, urging the Senate to hold a roll call vote to interrupt the Senate floor proceedings and postpone the committee’s consideration of Mr. Bolton.

“There are Democrats on the committee making unfounded allegations against Mr. Bolton,” a White House spokesman told The New York Sun yesterday. “We are happy to provide any additional information that the committee may need. We are confident that Secretary Bolton will be confirmed. The president believes John Bolton is the right man for the job.” The panel’s ranking Democrat, Senator Biden of Delaware, made the case that his committee needed more time to consider new allegations against Mr. Bolton that had come to his staff’s attention in recent days.

Specifically, Mr. Biden pointed to a letter from Melody Townsel, a former Usaid contractor in Kyrgyzstan who claims Mr. Bolton threatened her and threw objects at her in the hall of a Moscow hotel more than 10 years ago. The Sun reported Monday that Ms. Townsel was a founder of the Dallas chapter of “Mothers Opposing Bush.”

Mr. Biden initially called for a closed hearing, citing concerns about Mr. Bolton’s reputation, to discuss the allegations in Ms. Townsel’s letter. But on Saturday, Mr. Biden’s staff e-mailed the letter to journalists.

The Democratic attacks on Mr. Bolton did not end with the latest allegations from Ms. Townsel.

Mr. Biden said he wanted his staff to examine 10 intercepts from the National Security Agency in which Mr. Bolton requested the names of Americans speaking with foreigners. Mr. Biden also said he thought Mr. Bolton was lying to the committee when he said he visited CIA headquarters at the end of the business day in 2002 to discuss a national intelligence officer on Latin America. He said his log from that day proved that Mr. Bolton had in fact visited Langley in the morning.

Senator Coleman, a Minnesota Republican who is leading the Senate’s investigation into the U.N. oil-for-food program, as well as Messrs. Lugar and Allen, defended Mr. Bolton at the meeting. But few other Republican senators did.

After the committee’s meeting yesterday, Mr. Voinovich told some reporters, “I’m saying right now I want more information.”

A group supporting Mr. Bolton’s nomination, Move America Forward, announced yesterday it would be running radio advertisements in Ohio to portray Mr. Voinovich as an obstructionist.

“We are going to put our resources into putting the heat on Senator Voinovich until he sees the light,” the co-chairwoman of the organization, Melanie Morgan, said in a statement.

A friend of Mr. Bolton and former Pentagon adviser, Richard Perle, said yesterday that the delay in the vote was a “setback.” “It’s a setback, but it is by no means lost,” he said. “By all indications, the administration remains committed to Bolton’s nomination, and the United Nations is desperate for someone who can reform it.”

Another supporter of Mr. Bolton, Danielle Pletka, who is also a vice president at the American Enterprise Institute, yesterday said, “This is a disgrace, the idea that temperament is suddenly important. There are legions who have gone before John, as well as members of Congress, who have behaved appallingly.”