PARIS » More than a decade before the international agency that monitors chemical weapons won the Nobel Peace Prize, John R. Bolton marched into the office of its boss to inform him that he would be fired.

"He told me I had 24 hours to resign," said Josi Bustani, who was director general of the agency, the Organization for the Prohibition of Chemical Weapons in The Hague. "And if I didn’t I would have to face the consequences."

Bolton, then an undersecretary of state and later the U.S. ambassador to the United Nations, told Bustani that the Bush administration was unhappy with his management style.

But Bustani, 68, who had been re-elected unanimously just 11 months earlier, refused, and weeks later, on April 22, 2002, he was ousted in a special session of the 145-nation chemical weapons watchdog.

The story behind his ouster has been the subject of interpretation and speculation for years, and Bustani, a Brazilian diplomat, has kept a low profile since then. But with the agency thrust into the spotlight with news of the Nobel Prize last week, Bustani agreed to discuss what he said was the real reason: the Bush administration’s fear that chemical weapons inspections in Iraq would conflict with Washington’s rationale for invading it. Several officials involved in the events, some speaking publicly about them for the first time, confirmed his account.

Bolton insists that Bustani was ousted for incompetence. In a telephone interview Friday, he confirmed that he had confronted Bustani. "I told him if he left voluntarily we would give him a gracious and dignified exit," he said.

As Bustani tells the story, the campaign against him began in late 2001, after Iraq and Libya had indicated that they wanted to join the Chemical Weapons Convention, the international treaty that the watchdog agency oversees. To join, countries have to provide a list of stockpiles and agree to the inspection and destruction of weapons, as Syria did last month after applying. Inspectors from the agency were making plans to visit Iraq in late January 2002, he said.

"We had a lot of discussions because we knew it would be difficult," Bustani, who is now Brazil’s ambassador to France, said Friday in his embassy office in Paris. The plans, which he had conveyed to a number of countries, "caused an uproar in Washington," he said. Soon, he was receiving warnings from American and other diplomats.

"By the end of December 2001, it became evident that the Americans were serious about getting rid of me," he said. "People were telling me, ‘They want your head.’"

Bolton called on Bustani a second time. "I tried to persuade him not to put the organization through the vote," Bolton said.

But still Bustani refused, and his fate was sealed. The United States had marshaled its allies, and at an extraordinary session, Bustani was ousted by a vote of 48-7, with 43 abstentions. He was reportedly the first head of an international organization to be pushed out of office this way, and some diplomats said the pressure campaign had made them uneasy.

Bolton’s office had also circulated a document that accused Bustani of abrasive conduct and taking "ill-considered initiatives" without consulting with the United States and other member nations, diplomats said.

But Bustani and some senior officials, both in Brazil and the United States, say Washington acted because it believed that the organization under Bustani threatened to become an obstacle to the administration’s plans to invade Iraq. As justification, Washington was claiming that Saddam Hussein, the Iraqi leader, possessed chemical weapons, but Bustani said his own experts had told him that those weapons were destroyed in the 1990s, after the Persian Gulf war.

"Everybody knew there weren’t any," he said. "An inspection would make it obvious there were no weapons to destroy. This would completely nullify the decision to invade."

Bolton disputed that account. "He made that argument after we invaded," he said. Twice during the interview, Bolton said, "The kind of person who believes that argument is the kind who puts tin foil on his ears to ward off cosmic waves."

But diplomats in The Hague said officials in Washington had circulated a document saying that the chemical weapons watchdog under Bustani was seeking an "inappropriate role in Iraq," which was really a matter for the U.N. Security Council.

Avis Bohlen, a career diplomat who served as Bolton’s deputy before her retirement, said in a telephone interview from Washington on Saturday that others besides Bolton believed that Bustani had "stepped over some lines" in connection with Iraq and other matters. "The episode was very unpleasant for all concerned," she said.

Speaking from Sco Paulo, Brazil, on Saturday, Celso Lafer, the former Brazilian foreign minister, said that in early 2002, he was asked to meet privately with Secretary of State Colin L. Powell, who a year earlier had praised Bustani’s leadership in a letter.

Lafer said Powell told him, "’I have people in the administration who don’t want Bustani to stay, and my role is to inform you of this.’"

"It was a complicated process," Lafer recalled, "with the United States and particularly John Bolton and Donald Rumsfeld wanting the head of Bustani."

"My view," he continued, "is that the neocons wanted the freedom to act without multilateral constraints and, with Bustani wanting to act with more independence, this would limit their freedom of action."

Getting Bustani fired took some doing. Washington failed to obtain a no-confidence motion from the chemical weapons watchdog’s executive council. Then the United States, which was responsible for 22 percent of the agency’s budget at the time, threatened to cut off its financing and warned that several other countries, including Japan, would follow suit, diplomats have said.

Bustani recalled that the ambassador from Britain, one of the agency’s most committed member nations, told him that London had sent instructions to vote with Washington. With the United States and Japan covering almost half the budget, the organization ran the risk of collapsing, Bustani said.

On Friday, while fielding a flow of messages in his office, Bustani said he felt gratified about the Nobel Prize news and did not regret his days at the agency. "I had to start it from the beginning, create a code of conduct, a program of technical assistance," he said. "We almost doubled the membership."

He reflected on the contrast between Iraq and Syria. Inspectors from the agency are there now, cataloging the government’s stockpiles of chemical weapons as a step forward in Syria’s civil war, now in its third year.

"In 2002, the U.S. was determined to oppose Iraq joining the convention against the weapons, which it did not even have," he said. "This time, joining the convention and having the inspectors present is part of the Syrian peace plan. It is such a fundamental shift."

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