Sen. Richard Lugar, the Foreign Relations Committee chairman, talked at length about the controversy over Bolton, saying opponents have criticized him as "abrasive, confrontational and insensitive."
"In the diplomatic world, neither bluntness nor rhetorical sensitivity is a virtue in itself," the Indiana Republican said. "There are times when blunt talk serves a policy purpose; other times it does not."
Sen. John Kerry, D-Mass., said he had serious questions about Bolton's "commitment to the U.N."
"It is critical we have someone with respect for diplomacy, who believes in the United Nations despite its flaws," he said.
"I'm surprised the nominee wants the job he's been nominated for, given the many negative things he's had to say about the U.N.," Biden said.
Added Sen. Barbara Boxer, D-Calif., who aired excerpts from a 1994 Bolton speech to demonstrate what she said is his disdain for the U.N.: "You can dance around it, you can run away from it, you can put perfume on it, but the bottom line is the bottom line."
Three protesters briefly interrupted the proceedings, standing up in succession with pink T-shirts and banners, one reading: "Diplomat for hire. No bully please."
Critics of Bolton cite his comment from that 1994 speech that it would not matter if the top 10 stories of the 39-floor U.N. headquarters building in New York were lost.
"There's not a bureaucracy in the world that couldn't be made leaner," responded Bolton.
Committee Democrats also have circulated a portion of a 2-year-old Senate Intelligence Committee report questioning whether Bolton pressured a State Department intelligence analyst who tried to tone down language in a Bolton speech about Cuba's biological weapons capabilities.
According to committee aides who spoke on condition of anonymity, among critics being contacted by committee Democrats is Christian P. Westermann, a department intelligence officer who has clashed with Bolton.
Committee Democrats questioned whether Bolton tried to have Westermann's job portfolio changed as a result. Bolton said he had "lost trust in him and thought he should work on other accounts."
"There is nothing there, there, and I would put it all out on the public record — all of it," Bolton said.
In a recent interview with The Associated Press, Secretary of State Condoleezza Rice also defended Bolton, saying he is a good negotiator and would be great in the U.N. environment despite perhaps lacking subtlety.
Republicans control the Foreign Relations Committee by 10-8, and Lugar hopes for a vote on the nomination Thursday. Most, if not all, panel Democrats are expected to oppose the nomination. Bolton's nomination is also opposed by scores of retired American diplomats, who signed a letter to Lugar urging it be rejected.
"A lot will depend on how Sen. Lincoln Chafee, the Republican swing vote, will view the testimony by State Department and intelligence officials," said Falk.
Chafee spokesman Stephen Hourahan said the Rhode Island senator was leaning toward supporting Bolton "unless something surprising shows up" at the hearing.