WASHINGTON (AP) – Unable to win Senate confirmation, Ambassador Bolton will step down when his temporary appointment expires within weeks, the White House said Monday.

Mr. Bolton’s nomination has languished in the Senate Foreign Relations Committee for more than a year, blocked by Democrats and several Republicans. Senator Chafee, a moderate Republican who lost in the midterm elections Nov. 7 that swept Democrats to power in both houses of Congress, was adamantly opposed to Mr. Bolton.

Critics have questioned Mr. Bolton’s brusque style and whether he could be an effective public servant who could help bring reform to the U.N.

President Bush, in a statement, said he was “deeply disappointed that a handful of United States senators prevented Ambassador Bolton from receiving the up or down vote he deserved in the Senate.”

“They chose to obstruct his confirmation, even though he enjoys majority support in the Senate, and even though their tactics will disrupt our diplomatic work at a sensitive and important time,” Bush said. “This stubborn obstructionism ill serves our country, and discourages men and women of talent from serving their nation.”

Senator Kerry said Mr. Bolton’s departure could be a turning point for the administration.

“With the Middle East on the verge of chaos and the nuclear threats from Iran and North Korea increasing, we need a United Nations ambassador who has the full support of Congress and can help rally the international community to tackle the serious threats we face,” Kerry said. He said it was an opportunity for Bush to nominate an ambassador “who enjoys the support necessary to unite our country and the world and who can put results ahead of ideology.”

Mr. Bush gave Mr. Bolton the job temporarily in August 2005, while Congress was in recess. Under that process, the appointment expires when Congress formally adjourns, no later than early January.

The White House resubmitted Mr. Bolton’s nomination last month. But with Democrats capturing control of the next Congress, his chances of winning confirmation appeared slight. The incoming chairman of the Senate Foreign Relations Committee, Senator Biden, said he saw “no point in considering Mr. Bolton’s nomination again.”

While Mr. Bush could not give Mr. Bolton another recess appointment, the White House was believed to be exploring other ways of keeping him in the job, perhaps by giving him a title other than ambassador. But Mr. Bolton informed the White House he intended to leave when his current appointment expires, White House deputy press secretary Dana Perino said.

Mr. Bush planned to meet with Mr. Bolton and his wife later Monday in the Oval Office.

Mr. Bush said he accepted Mr. Bolton’s decision with deep regret.

“He served his country with extraordinary dedication and skill, assembling coalitions that addressed some of the most consequential issues facing the international community,” the president said. “During his tenure, he articulately advocated the positions and values of the United States and advanced the expansion of democracy and liberty.

“Ambassador Bolton led the successful negotiations that resulted in unanimous Security Council resolutions regarding North Korea’s military and nuclear activities. He built consensus among our allies on the need for Iran to suspend the enrichment and reprocessing of uranium,” Mr. Bush added. “His efforts to promote the cause of peace in Darfur resulted in a peacekeeping commitment by the United Nations. He made the case for United Nations reform because he cares about the institution, and wants it to become more credible and effective.”

Mr. Bolton, who pushed strongly for U.N. reform, has had strained relations with many in the U.N. Secretariat, led by Secretary-General Annan, and has repeatedly called for all top U.N. officials to leave when Annan steps down as U.N. chief on Dec. 31 and is replaced by Ban Ki-moon.

“I think Ambassador Bolton did the job he was expected to do,” Mr. Annan said Monday morning when asked about Bolton’s resignation. “He came at a time when we had lots of tough issues from reform to issues on Iran and North Korea. I think as a representative of the U.S, government, he pressed ahead with the instructions he had been given and tried to work as effectively as he could.”

As late as last month, Mr. Bush, through his top aides, said he would not relent in his defense of Mr. Bolton, despite unwavering opposition from Democrats who view Mr. Bolton as too combative for international diplomacy.

In a letter to Mr. Bush, dated last Friday, Mr. Bolton offered no reason for his decision. “After careful consideration, I have concluded that my service in your administration should end when the current recess appoint expires,” Mr. Bolton wrote.