WASHINGTON – President Bush yesterday called for the Senate to “put aside politics” and confirm John Bolton as U.N. ambassador, signaling that the White House will not walk away from its nominee.

“John’s distinguished career and service to our nation demonstrates that he is the right man at the right time for this important assignment,” Mr. Bush said in a speech before the Independent Insurance Agents and Brokers of America convention yesterday. “I urge the Senate to put aside politics and confirm John Bolton to the U.N.”

But as the president expressed his personal support for Mr. Bolton, the Senate Foreign Relations Committee continued its investigation into his temperament, expanding the list of bureaucrats who worked with the current undersecretary of state for arms control and international security affairs. The committee must confirm Mr. Bolton before his nomination heads to the full Senate.

The White House has described the accusations voiced by Democratic lawmakers in the last two weeks as “unfounded allegations.” Nonetheless, the Democrats’ case impressed Senator Voinovich, a Republican from Ohio, enough Tuesday that he said he could not vote for Mr. Bolton, whose nomination was expected to pass the committee along party lines.

Instead of approving Mr. Bolton’s nomination, the committee’s chairman, Senator Lugar, a Republican from Indiana, reluctantly agreed to postpone the vote until next month. The delay has given the committee’s staff more time to investigate a series of allegations that Mr. Bolton not only yelled at underlings, but that he did so to pressure analysts to change intelligence estimates with which he did not agree.

This week, committee staff interviewed a former American ambassador to South Korea, Thomas Hubbard. In his testimony earlier this month, Mr. Bolton said Mr. Hubbard had congratulated him on a July 31, 2003, speech he gave denouncing North Korea leader Kim Jong Il as a “tyrannical dictator.” Some Senate Democrats have suggested the speech from Mr. Bolton was a deliberate attempt to scuttle six-party talks with Pyongyang over their declared nuclear weapons program. At the time, the North Korean press denounced Mr. Bolton as “human scum.”

In an interview with Newsweek, Mr. Hubbard said he only congratulated Mr. Bolton because he made changes to correct factual errors in the speech. Mr. Hubbard contacted the committee to say he did not think the bellicose tone of the speech was particularly helpful to his diplomatic efforts.

However, Mr. Hubbard’s boss at the time, Secretary of State Powell, in an August 26, 2003, letter to Senator Kyl, a Republican from Arizona, said the text of Mr. Bolton’s remarks was fully cleared by the department .”It was consistent with administration policy, did not really break new ground with regard to our disdain for the North Korean leadership and, as such, was official,” he wrote in the letter, which has been included in evidence collected by the committee.

Mr. Powell has reportedly had recent private conversations with two Republican senators whose support for Mr. Bolton has flagged – Senator Chafee from Rhode Island and Senator Hagel from Nebraska – in which Mr. Powell offered a mixed assessment of Mr. Bolton. Mr. Powell’s former chief of staff, Lawrence Wilkerson, told the New York Times earlier this week that he thought Mr. Bolton would be a terrible ambassador to the United Nations.

A spokesman for Ms. Chafee told Bloomberg news service yesterday that his boss was “much less likely” now to vote for Mr. Bolton, but he added that he was now fully engaged in examining the nominee’s record.

On CNN yesterday, Senator Dodd, a Connecticut Democrat who has been leading the charge against Mr. Bolton, boasted that the committee had interviewed seven people who have contradicted Mr. Bolton’s contention that he did not seek to have two intelligence analysts fired. On the same show, Senator Coleman, a Republican from Minnesota and a strong Bolton supporter, said Mr. Dodd’s characterization of Mr. Bolton’s original testimony was wrong. He noted that Mr. Bolton admitted to asking the two analysts to change portfolios.

The two analysts in question, Christian Westermann and Fulton Armstrong, have already granted interviews to the Senate Foreign Relations Committee. Both men disagreed with language in a May 2002 speech that Mr. Bolton gave to the Heritage Foundation warning of Cuba’s biological weapons program.

In the end, the language Mr. Bolton used for the Cuba speech was nearly identical to testimony a former assistant secretary of state for intelligence and research, Carl Ford Jr., had given to the Senate Foreign Relations Committee two months earlier. Mr. Ford testified against Mr. Bolton last Tuesday.