The International Atomic Energy Agency and its director, Mohamed ElBaradei, won the 2005 Nobel Prize for Peace yesterday for their efforts to prevent the spread of atomic weapons and promote the peaceful use of nuclear energy.

The award for the 63-year-old ElBaradei and his army of international inspectors was seen within the U.N.-sponsored organization as a vindication of its work in Iraq before the war and currently in Iran, where they are leading a cautious investigation of that country's nuclear program while promoting diplomacy as a way of resolving the crisis there.

In announcing its selection yesterday at a ceremony in Oslo, the Norwegian Nobel Committee said ElBaradei "stood as an unafraid advocate" for disarmament, relying on diplomacy, rather than confrontation, to rid the world of nuclear threats.

"At a time when disarmament efforts appear deadlocked, when there is a danger that nuclear arms will spread both to states and to terrorist groups, and when nuclear power again appears to be playing an increasingly significant role, IAEA's work is of incalculable importance," it said.

ElBaradei, who opposed the U.S.-led invasion of Iraq and spent the last year fending off attempts by the White House to push him out of the agency, said he was "humbled" and strengthened by what he saw as an international vote of confidence in an agency that has been battered by conflict with Washington.

"I hope this will enhance our credibility and our visibility and that our word will be taken for what it is," he said in a telephone interview yesterday from his home in Vienna. He said he was tremendously proud of his 2,000-member staff, including those who have worked on a string of high-profile nuclear investigations in Iraq, Iran, North Korea and Libya.

"They have been through a hard time, they've taken hits from many corners and have been accused of being biased. I think this is a wonderful recognition of their honesty, their impartiality and their integrity," he said.

One year ago, the Bush administration was waging a vigorous but solitary campaign to oust ElBaradei -- including a complete halt of intelligence sharing with the agency, recruitment of potential replacements and eavesdropping on his calls in search of ammunition to use against him.

The United States helped install ElBaradei in his job eight years ago, but his refusal in 2003 to confirm White House allegations that Iraq had rebuilt its nuclear weapons program lost ElBaradei the American support he had enjoyed.

When he began openly resisting U.S. calls to intensify pressure on Iran, Washington responded by trying to prevent him from taking a third term as agency director. But the effort, led by John R. Bolton, who was in charge of nuclear issues during President Bush's first term, was abandoned in June when no candidate emerged to challenge ElBaradei.

Bolton, now U.S. ambassador to the United Nations, offered a tepid response to the announcement, saying only that he shared in the congratulations offered by Secretary of State Condoleezza Rice. Asked by reporters whether he saw the prize as a rebuff to U.S. strategy, Bolton said: "I'll stick with the secretary's statement."

Rice called ElBaradei yesterday to congratulate him and issued a warm statement praising the agency's work and pledging continued cooperation.

Nobel Committee Chairman Ole Danbolt Mjoes, in making the announcement beneath crystal chandeliers in a small vaulted room at the Norwegian Nobel Institute in Oslo, denied the award was meant as a slap at the Bush administration. "This is not a kick in the legs to any country."

But some were unconvinced.

"I've got to believe that the role ElBaradei personally played, and the agency played, in the build-up to the war in Iraq was a major factor in the committee's decision," said Joseph Cirincione, a nuclear expert at the Carnegie Endowment for International Peace. "ElBaradei was pleading to give inspectors more time, he was on the verge of declaring that Iraq had not reconstituted its nuclear weapons program, which was the major justification for the war, and we now know he was right."

Others suggested the committee sought to bolster ElBaradei as he attempts to navigate a crisis with Iran, which says the nuclear program it built in secret is aimed at producing energy, not bombs. No proof of a weapons program has been found, but the United States and other governments believe Iran should face the threat of U.N. sanctions for concealing its activities. "The message here is that diplomacy is the best approach to take in dealing with tough proliferation cases," said Charles Ferguson with the Council on Foreign Relations.

Despite disagreements over Iraq, Bush administration officials acknowledge that the IAEA's Iran investigation, in its third year, has been thorough and that the agency has uncovered far more than U.S. intelligence could have learned without it.

But ElBaradei has faced criticism for stepping beyond his mandate, playing diplomatic mediator when many officials in Washington and beyond want him and his agency to make more decisive and hard-nosed pronouncements on Iran and other nuclear threats.

"Mohamed really has a more political profile than many people expect of a technical agency," said Robert Einhorn, assistant secretary of state for nonproliferation until 2001. "When he steps outside his appropriate role but in favor of a U.S. policy, we applaud him. But when we don't like this recommendations, we put him in the doghouse," Einhorn said.

As the recipient of what many consider the world's most prestigious award, ElBaradei joins a winners list that includes Woodrow Wilson, Martin Luther King, Nelson Mandela, the Dalai Lama, Jimmy Carter, Mother Teresa and a host of agencies connected, like the IAEA, with the United Nations, including the United Nations itself and Secretary General Kofi Annan. ElBaradei and the agency will share about $1.3 million in prize money.

Nuclear weaponry and peacemaking have been consistent themes of the awards, created by the will of Alfred Nobel, the Swede given credit for the development of dynamite.

The Vienna-based IAEA, established under United Nations auspices in 1957, coordinates nuclear safety around the world and monitors materials that could be diverted for weapons use. It has played pivotal investigative roles in four major crises in recent years: Iran, Iraq, North Korea and the nuclear black market run by one of Pakistan's top scientists.

International Atomic Energy Agency workers in Vienna celebrate the announcement from the Nobel Committee.Mohamed ElBaradei and spokeswoman Melissa Fleming go to a news conference after learning of the award.