WASHINGTON – A former State Department intelligence chief yesterday called John Bolton a “serial abuser” of analysts with whom he disagreed, criticism that Democrats said bolstered the case for rejecting the president’s nominee for ambassador to the United Nations.

Despite that testimony, however, the key undecided Republican on the Senate Foreign Relations Committee yesterday said he was inclined to vote for Mr. Bolton. “‘Serial abuser’ is strong words, but we didn’t get the evidence,” Senator Chafee, a Republican of Rhode Island, said. “It’s all one incident.”

That one incident was examined in excruciating detail yesterday as the Senate panel heard testimony from a former assistant secretary of state for intelligence and research, Carl Ford. Mr. Ford, who described himself as a “loyal Republican,” said Mr. Bolton had yelled at one of his analysts, Christian Westermann, in February 2002 after he had asked him to clear intelligence on Cuba’s biological weapons programs for a speech he proposed to give at the Heritage Foundation.

“I’ve never seen anything like this in terms of abusing little people,” Mr. Ford said. “It’s an 800-pound gorilla devouring a banana.” He also said Mr. Bolton was a “kiss-up, kick-down kind of guy.”

On Monday, Mr. Bolton insisted that he never tried to get Mr. Westermann fired, but he admitted talking to Mr. Ford and Mr. Ford’s principle deputy, Tom Fingar, about getting him transferred to a different portfolio.

Mr. Bolton maintained that Mr. Westermann exceeded his job description by voicing his dissent on the proposed speech to the CIA and not to Mr. Bolton.

In his defense, Mr. Bolton pointed to an e-mail from Mr. Fingar at the time that said, “It won’t happen again.”

Mr. Ford, however, said that Mr. Westermann was within his rights. While he said he did not remember all of the details of his hallway conversation with Mr. Bolton three years after the senior State Department staff meeting, Mr. Ford did say that the gist of the conversation, to his recollection, was that Mr. Bolton wanted Mr. Westermann fired.

While Mr. Ford’s testimony was before the entire Senate Foreign Relations Committee, in some ways it was directed at Senator Chafee. The Rhode Island Republican holds the key swing vote on the committee considering Mr. Bolton’s nomination. It could vote as soon as tomorrow. So far, Mr. Chafee, whose home state went to John Kerry in the 2004 presidential elections, has not said definitively how he will vote. “I am going to talk with my colleagues,” he said after the hearing. “But I’m inclined to vote for him.”

Democrats yesterday said Mr. Ford’s testimony persuaded them that they would have been justified halting Mr. Bolton’s nomination in committee.

“If this isn’t enough, I don’t know what you can do,” Senator Dodd, a Democrat from Connecticut, told the Associated Press after the hearing.

Republicans on the Senate panel were respectful of Mr. Ford, but they also questioned his assessment that Mr. Bolton had displayed a pattern of intimidating intelligence analysts. At one point, Senator Coleman, a Republican from Minnesota who is leading the Senate’s investigation into the U.N. oil for food program, said Mr. Ford’s testimony would likely not stand up in a court of law.

Senator Obama, a Democrat from Illinois, drew a connection between Mr. Bolton’s pressure on Mr. Westermann and the failure of the intelligence community to accurately assess the threat of weapons of mass destruction in Iraq. He said Mr. Bolton “is intimidating intelligence officers so that the facts will fit his positions, which is exactly what the debate was about with respect to the Iraqi war.”

Mr. Ford, however, said in the hearing, “I can’t lay on Secretary Bolton the intelligence community’s failure.” He added, “It had nothing to do with Bolton.”

Some Democratic staffers had initially looked into allegations that Mr. Bolton may have pressured underlings to include a line in a State Department fact sheet before the Iraq war that alleged Saddam Hussein’s regime tried to procure uranium from Niger. In the House, Rep. Henry Waxman, a Democrat from California, wrote a letter to the State Department asking for e-mail between Mr. Bolton and his staff before they produced the fact sheet. On Monday and Tuesday, the incident did not come up.

After the hearing, Senator Martinez, a Florida Republican, said of the Democrat’s effort against Mr. Bolton, “I think he’s been confirmed so many times, and the Democrats have voted for him so many times, it is a matter of finding something new on him.”