President Bush's selection of Bolton last month has stirred controversy because of his expressions of disdain for the United Nations and the blunt criticism he has leveled at North Korea and other countries and arms control treaties.
Bolton, 56, has served in the past three Republican administrations and been one of his party's strongest conservative voices on foreign affairs issues. He is now the administration's arms control chief.
In a recent interview with The Associated Press, Secretary of State Condoleezza Rice defended Bolton by saying that "not everybody is given to subtlety and indirection." She said Bolton is a good negotiator and would be great in the U.N. environment.
Republicans control the Foreign Relations Committee by 10-8, but most if not all panel Democrats are expected to oppose the nomination. One of them, Sen. Bill Nelson, D-Fla., said Bolton has not been an effective arms negotiator and speaks to people in a condescending, inflammatory way.
"That's not the kind of representative of America that we want in the United Nations," Nelson said.
"The lobbying for and against Bolton has been intense, with serious talk of a filibuster if the nomination gets out of Committee on to the Senate floor," said CBS News Foreign Affairs Analyst Pamela Falk. "The good news is that it means that the nomination of the U.S. Ambassador to the U.N. matters, and that is more of a statement about the strong position of the U.S. at the U.N."
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.
On television talk shows Sunday, committee Democrats Christopher Dodd of Connecticut, Joe Biden of Delaware and Jay Rockefeller of West Virginia cited the alleged pressure and other alleged incidents as among reasons they will oppose Bolton's nomination.
Committee Chairman Richard Lugar, R-Ind., hopes for a vote on Bolton's nomination Thursday. A tie could keep the panel from recommending Senate approval.
"At the Committee Hearing on Monday, a lot will depend on how Senator 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.
In preparations for the hearings, Democrats led by Biden have questioned Bolton's views on intelligence. They were granted access to four State Department officials and were permitted to examine some of its documents.
But Biden's spokesman, Norm Kurz, complained the Democrats were not given everything they requested and were allowed only limited time for the interviews and only Friday to look at the papers.
Carl W. Ford Jr., a former chief of the department's bureau of intelligence and research with whom Bolton apparently clashed, was scheduled to testify on Tuesday.
Since his nomination, Bolton has promised to work closely with other countries and members of Congress and said he has always supported "effective multilateral diplomacy."
As assistant secretary of state for international relations under the first President Bush, he helped organize the alliance that forced Iraq out of Kuwait.
Critics, though, recall his 1994 comment that it would not matter if the top 10 stories of the 39-floor U.N. headquarters building in New York were lost.
He has said there is "no such thing as the United Nations," and asserted that the United States is the only real authority the world has. He has also questioned whether the organization undertakes too many peacekeeping missions.
In February, he sharply criticized China for selling missile technology to Iran and other countries. He has been critical of Europe's efforts to reach an agreement with Iran to curb that country's nuclear program.
During administration efforts two years ago to seek an agreement with North Korea over its nuclear program, Bolton called that country's leader a "tyrannical dictator." North Korean officials refused to deal with him.
Bolton helped lead U.S. opposition to the International Criminal Court and the United States' eventual withdrawal from the treaty creating the court.
His opponents have accused him of claiming without evidence that Syria and Cuba were trying to develop biological weapons.
Bolton would replace John Danforth, a former Republican senator from Missouri, who resigned after half a year as U.N. ambassador.