NEW YORK - Former US Secretary of State Colin Powell was more skeptical about the evidence he used in an impassioned 2003 speech at the United Nations Security Council to justify the American-led invasion than previously known, according to a new memoir by Kofi Annan.

Six weeks after the Iraq invasion, Annan wrote, Powell visited his 38th-floor office at the United Nations to privately exult with him over news that American forces believed they had found mobile laboratories in Iraq that the administration claimed were used by Saddam Hussein to make weapons of mass destruction - the core reason for the war, according to a dispatch published in The New York Times Thursday.

“Kofi, they’ve made an honest man of me,” Annan quoted Powell as telling him. Annan wrote that “the relief - and the exhaustion - was palpable. I could not help but smile along with my friend, and wanted to share in his comfort,” even though Annan himself was far from convinced. Still, Annan wrote, “I could only be impressed by the resilience of this man, who had endured so much to argue for a war he clearly did not believe in.”

Efforts to reach Powell for comment about the passage were not immediately successful, the Times said. Peggy Cifrino, his office assistant, was cited as saying he was traveling and contacting her only intermittently.

No weapons of mass destruction were ever found in Iraq. Powell’s role, which some historians say irreparably harmed his credibility and derailed his political career, has also been well documented in several books on the Iraq war. “But the encounter between Mr. Powell and Mr. Annan, as reprised by the former secretary general, offered a new insight into the degree of doubt harboured by Mr. Powell about putting troops on the ground in Iraq,” the Times said.

The book will go on sale on Tuesday — the Times obviously got an advance copy.

In a telephone interview with The Times from his Geneva office,  Annan, 74, said he had decided to use that anecdote in the opening chapter of his new book, “Interventions: A Life in War and Peace,” published by The Penguin Press, because Iraq had been such an important issue during his tenure, which lasted from 1997 through the end of 2006. The Iraq war, he said, was “an event that divided the international community hopelessly - the way Syria is about to do.”

Moreover, Annan said, he regarded Mr. Powell as “a friend, highly respected, a star among the foreign ministers. And I think the presentation of the U.S. case to the council did a bit of harm to him, and I wanted to convey what happened at the time.”

The book, written in collaboration with Nader Mousavizadeh,  Annan’s former adviser and speechwriter, is a chronicle of his diplomatic life. Born in Ghana, Annan is the first career United Nations official and first sub-Saharan African to rise to the post of secretary general. He was awarded the Nobel Peace Prize in 2001 for his work at the United Nations.

Written as part autobiography, part history lesson, it is infused with  Annan’s accounts of private encounters with world leaders, including  Hussein of Iraq, with whom he once had an intense exchange in Baghdad, convincing him to allow weapons inspectors into Hussein’s presidential palaces, the Times said.

The book is also Annan’s effort to explain the circumstances behind some spectacular lapses that have been partly attributed to Annan during his tenure as secretary general and earlier, when he ran the department in charge of United Nations peacekeeping operations.

Annan wrote that the reasons behind the United Nations failure to avert the 1994 Rwanda genocide, to take one example, were rooted in earlier peacekeeping debacles in Somalia and Haiti. Many nations that had contributed peacekeepers, led by the United States, developed an aversion to taking such risks, Annan wrote, and the Security Council resisted ordering measures that might include the use of force. “Fatefully, the first operation to be created in this climate was the mission to Rwanda.”

In what may be a surprise to some of Annan’s conservative critics, The Times said Annan expressed great admiration in the book for President George W. Bush, despite their disagreements on the Iraq war and what  Annan regarded as Bush’s flawed approach to the Israeli-Palestinian conflict. Annan said Bush’s effort to combat the global AIDS epidemic represented “the biggest financial commitment by any country in history to fight a single disease.”

Annan said he had been working on the memoir for two years and was nearly finished this past winter when he got a telephone call from Ban Ki-moon, his successor as secretary general, with an extraordinary request.

Ban wanted Annan to negotiate a diplomatic solution to the Syria uprising, as a special envoy representing the United Nations and the Arab League, where exasperation with President Bashar al-Assad of Syria seemed intractable.

Ban said he was asking on behalf of a group of foreign ministers, who believed that Annan’s negotiating skills could succeed in Syria.

Annan, who had dealt with Syria’s president before, consented, and the book was delayed, with the final pages to be revised.

“We had been on the verge of delivering it to the editors,”  Annan was quoted as saying.

The Syria portion of the book, which goes on sale Tuesday, was updated to include a tenuous cease-fire that Annan negotiated in March. Annan has since resigned. Since then, the conflict has worsened. The 300 United Nations monitors who were to observe his cease-fire have left Syria, and a new special envoy, Lakhdar Brahimi, who once worked for Annan, has now been designated his successor.

Still, Annan said, he had decided awhile ago that he would make no further revisions to the book. Now, he said, “people are asking me if I’ll write a second book, about Syria.”

Annan said that in his multiple meetings with Assad in Damascus, he felt that he never got through to him. “Initially I felt he was in denial,” Annan said. “He felt like most of his problems were being caused by outsiders. If outsiders were to leave Syria alone, they would resolve their problems in no time.”

Leaders like Assad, he said, “tend to believe in the world they create.”