Former White House press secretary Scott McClellan has charged in an explosive new book that President George W Bush shaded the truth and manipulated public opinion to make the case for the "unnecessary" Iraq war.

McClellan, the first Bush insider to write a book criticizing his former boss and fellow Texan, drew instant condemnations on Wednesday from former White House colleagues who wondered why he stayed on the job.

"If he thinks he's going to ingratiate himself to his critics, he's sorely mistaken, and unfortunately, the only friends he had, he just lost," said Dan Bartlett, who served as White House counselor.

McClellan, in "What Happened -- Inside the Bush White House and Washington's Culture of Deception," presents himself as a one-time true Bush believer who mistakenly fell in line behind "the campaign to sell the war" in Iraq.

McClellan, who had argued strenuously from the White House podium on why the war was justified, wrote that the decision to go to war in Iraq was a "fateful misstep."    

"What I do know is that war should only be waged when necessary, and the Iraq war was not necessary," he said.

McClellan called Bush "a man of personal charm, wit, and enormous political skill," and "plenty smart enough to be president," while sprinkling criticism of him throughout the 341-page book.

Bush led a "carefully orchestrated campaign to shape and manipulate sources of public approval to our advantage" to get Americans behind the war."    

His operating style, said McClellan, was to remain "continually in campaign mode, never explaining, never apologizing, never retreating. Unfortunately, that strategy also had less justifiable repercussions: never reflecting, never reconsidering, never compromising. Especially where Iraq was concerned."    

McClellan was replaced as White House press secretary in 2006 by Tony Snow, and Snow gave way to Dana Perino about a year ago.

Many in the White House were stunned by the book. Perino blasted McClellan.

"Scott, we now know, is disgruntled about his experience at the White House. For those of us who fully supported him, before, during and after he was press secretary, we are puzzled. It is sad -- this is not the Scott we knew," she wrote in an e-mail to reporters.

"The book, as reported by the press, has been described to the president. I do not expect a comment from him on it -- he has more pressing matters than to spend time commenting on books by former staffers," she said.

The Iraq war was fought over charges that Saddam Hussein possessed weapons of mass destruction, which were never found.

Bush began building the case for war in 2002 after the upheaval caused by the Sept. 11, 2001, attacks.

McClellan, in a chapter called "Selling the War," said Bush and his top aides did not think through the implications of the conflict.

He said Bush and aides did not employ out-and-out deception, but rather participated in "shading the truth, downplaying the major reason for going to war and emphasizing a lesser motivation that could arguably be dealt with in other ways (such as intensified diplomatic pressure)."    

Bush, at the US Air Force Academy in Colorado, ignored the book and instead sought Americans' patience for the prolonged wars in Iraq and Afghanistan.

But former McClellan associates were livid. "Here's a guy who rode the president's coattails to the world stage and now is (urinating) on his political grave, all the way to the bank," said former White House deputy press secretary Trent Duffy.

Bartlett said McClellan was drawing broad conclusions from decisions in meetings that he did not attend. In the run-up to the war, McClellan was a deputy press secretary dealing with domestic affairs.

"Whatever misgivings Scott now proclaims to have