According to journalists who have read the book, Plan of Attack, author Bob Woodward says planning began in December 2001, even as the President said he was seeking a diplomatic solution to Iraq's stand-off with the United Nations.

The Washington Post, where Mr. Woodward is an editor, reports the book describes how the growing commitments required of the military, the CIA and U.S. allies during the planning phase made the decision difficult, in not impossible, to reverse.

The book will be released next week and is based on interviews with some 75 people involved in the planning of the war, including President Bush.

Asked about the reports Friday President Bush told reporters he could not remember the exact dates he asked for planning to begin.

Plan of Attack is also reported to address Mr. Bush's concern about world reaction to a war. The Associated Press, which obtained an advance copy, says that to preserve secrecy, the president kept details of the planning even from members of his own national security team.

The Washington Post report says Mr. Woodward outlines the tension between Vice President Dick Cheney, described in the book as a "steamrolling force" for war, and Secretary of State Colin Powell, who is said to have opposed it. The Post says Plan of Attack recreates how the two were so at odds over the conflict that they were barely on speaking terms.