But the chairman of the Senate Foreign Relations Committee, Sen. Richard Lugar, R-Ind., said Bolton was the president's "instrument of reform" for the United Nations and his bluntness should not disqualify him from serving.
Lugar said he would vote to confirm Bolton, but committee Democrats who appeared on the Sunday talk shows said they expected to go against the president.
The committee, with a 10-8 Republican majority, planned a Monday morning hearing on Bolton, who has served in the past three Republican administrations and has been one of the strongest conservative voices on foreign affairs.
Senate Democrats have circulated a portion of a two-year-old Senate Intelligence Committee report questioning whether Bolton pressured a State Department intelligence analyst who tried to tone down language in a 2002 speech on Cuba. In that speech, Bolton said Cuba was trying to develop biological weapons and was transferring its technical expertise to countries hostile to the United States. At the time, some officials said the information should not have been publicly disclosed. Cuba has denied the weapons allegation.
Bolton, the undersecretary of state for arms control and international security, has stirred controversy because of his gruffness, occasional outbursts, opposition to a number of treaties and outspoken criticism of the United Nations.
"I appreciate that many people have views about John Bolton's personality, his bluntness, the way that he handles himself," Lugar said in a broadcast interview.
"These are not, in my judgment, disqualifiers for a presidential nominee who is going to the U.N. to create reform," Lugar said.
But Sen. Joseph Biden, D-Del., said in a broadcast interview he would not vote to confirm Bolton. He said at a time when the president is relying more on U.N. cooperation with U.S. efforts in the Sudan and the Middle East, "I think it's a bad idea to have a man there who doesn't have much regard for the U.N."
When Senate Democratic leader Harry Reid of Nevada was asked if he would consider joining a filibuster on the president's nominee, he told CBS's "Face the Nation" he didn't know.
"He doesn't appear to be the best guy for the job, but let the committee work on this," Reid said.
Sen. Rick Santorum, R-Pa., had words of praise for Bolton, saying he had an "exemplary record."
"I think he's the right man for the U.N. because he brings the kind of candor that you need to an organization that's got a lot of trouble, does not have a lot of support here in the United States, does not have a lot of support in the Congress, particularly the Republican side," Santorum said in a broadcast interview.
"And I think having a man of that kind of strength is going to be an important thing for the U.N. to regain its credibility in the Congress."
Sen. Christopher Dodd, D-Conn., said he thought there was very credible information that Bolton tried at least twice to have intelligence analysts removed from their jobs because he was going to state a position which contradicted the information that the intelligence community believed was correct.
"If in fact he tried to have people dismissed because he did not like the analysis, then I don't think he's qualified to serve," Dodd said in a broadcast interview.
If confirmed, Bolton would succeed former Sen. John Danforth.