WASHINGTON – John Bolton will present his diplomatic credentials today to the U.N. secretary-general, Kofi Annan, after President Bush defied Democratic opposition and appointed his former undersecretary of state to be America’s ambassador to the United Nations.

At the White House yesterday, Mr. Bush derided a “handful of senators” for denying Mr. Bolton an “up-or-down vote in the Senate,” referring to two filibusters Democrats launched this spring when they demanded National Security Agency intercepts that Mr. Bolton requested in his tenure at Foggy Bottom.

“This post is too important to leave vacant any longer, especially during a war and a vital debate about U.N. reform,” the president said yesterday with Mr. Bolton standing beside him. “I’m sending Ambassador Bolton to New York with my complete confidence.” Just hours later, Mr. Bolton reported for work at the U.S. Mission in New York.

Democratic leaders reacted with anger to the recess appointment, which came 145 days after Mr. Bush first nominated Mr. Bolton. Senator Biden, a Democrat of Delaware who led his party’s campaign against Mr. Bolton in the spring, yesterday called the move “an abuse of power.” Under the Constitution, Mr. Bolton’s appointment will last until a newly elected Congress takes office in January 2007.

“Sending John Bolton to the U.N. behind the Senate’s back is a mistake in every respect. The reason John Bolton didn’t get a vote in the Senate is because the administration refused to provide information to which no one disputes the Senate is entitled,” Mr. Biden said.

Other Democrats questioned how effective Mr. Bolton would be in light of the fact that he lacked confirmation from the Senate. But Mr. Annan yesterday said he did not think it would be a problem. “I think it is the president’s prerogative, and the president has decided to appoint him through this process,” he said. “From where I stand, we will work with him as the representative of the president and the government.”

Mr. Annan also offered a bit of free advice to the new envoy, who has been criticized for his bluntness and undiplomatic style. “An ambassador always has to remember that there are 190 others who will have to be convinced, or a vast majority of them, for action to take place,” he said.

After sending Mr. Bolton’s nomination to the full Senate without its recommendation in May, the Senate Foreign Relations Committee formally asked the administration to provide it with copies of the National Security Agency intercepts Mr. Bolton requested during his time as undersecretary of state for arms control and international security. Mr. Biden and Senator Dodd, a Democrat of Connecticut, alleged these intercepts could prove that Mr. Bolton was seeking incriminating information on his colleagues in government.

After a briefing by the Directorate of National Intelligence, the chairman and ranking member of the Senate Select Committee on Intelligence wrote letters that said they found nothing untoward about Mr. Bolton’s requests. Nonetheless, even those two lawmakers were not allowed to see the actual intercepts made available to Mr. Bolton.

After requesting the information again, Democrats succeeded in getting 43 members of their own party and Senator Voinovich, a Republican from Ohio, to support a filibuster to block the debate. Mr. Voinovich was so opposed to Mr. Bolton’s nomination that he nearly cried in his floor speech recommending his colleagues vote against him.

Two administration officials yesterday said Mr. Bolton and Senate Majority Leader Frist, a Republican from Tennessee, privately urged the White House to release the intelligence. Ultimately, however, the president’s advisers did not want to release the privileged documents for the Bolton nomination, which could have set a problematic precedent for the administration in the pending Senate battle over Judge John Roberts’s nomination for the Supreme Court.

Not everyone agreed with the strategy. “I still don’t know why we didn’t just release the documents,” one administration official told The New York Sun yesterday.

While the NSA request was ultimately what sunk Mr. Bolton’s prospects for an up-or-down Senate vote, it was only the most recent in a series of questions Democrats and some Republicans raised about his fitness for the ambassadorship in a bruising nomination battle.

Throughout the spring, Democrats interviewed many of Mr. Bolton’s former colleagues who contended he was abusive to underlings, sought to pressure intelligence analysts, and was not forthcoming in his answers to questions from members of the Senate Foreign Relations Committee. His defenders on that panel questioned the credibility and motivations of Mr. Bolton’s accusers, such as a former USAID contractor, Melody Townsel, who went on to become a founder of the Dallas chapter of Mothers Opposing Bush after she worked with Mr. Bolton.

The high-profile nomination fight appeared to catch the White House off guard as a handful of Republicans wavered on the nomination in early spring. Then, after not attending any of the prior nomination hearings, Mr. Voinovich delayed the first vote in the Senate Foreign Relations when he surprised his colleagues and the White House by announcing he did not feel confident in voting Mr. Bolton out of the committee in what was expected to be a party-line vote.

Yesterday, a former senator and ambassador to the United Nations, John Danforth, told the Sun that he did not think the battle over Mr. Bolton’s nomination would hinder his performance at Turtle Bay. “We had to do it,” Mr. Danforth said, referring to the short staff of the U.N. mission in New York. “I don’t think the people around the U.N. ask an ambassador, ‘What was your confirmation process?'” Mr. Danforth added. If an ambassador “has to speak for the president, the president has to be comfortable with that person,” Mr. Danforth said.

In Washington, some of Mr. Bolton’s supporters reacted to the recess appointment with mild disappointment. The vice president for foreign and defense policy studies at the American Enterprise Institute, Danielle Pletka, yesterday said, “I don’t think this is a win or a loss. I think the Democrats have manipulated the system and badly served the interests of the United States. If, in fact, John had not gotten 56 votes, then I would have found their arguments more credible. He should have been confirmed. This was a matter of political muscle-flexing.”

The president of the Center for Security Policy, Frank Gaffney, however, saw the recess appointment of his friend Mr. Bolton as a positive development. “The bad guys are gnashing their teeth and the good guys are celebrating. It’s a win,” he said. “I would have preferred to get him confirmed. In the grand scheme of things, it is not going to matter. Aside from the abuse he took in this process, which was unwarranted, it came out okay.”