Former White House press secretary Scott McClellan, left, with President Bush in April 2006. (Ron Edmonds/Associated Press)

In a scathing new book, a Washington insider calls President George W. Bush to task for selling the war in Iraq with a "political propaganda campaign."

Scott McClellan, a former White House press secretary, is first out of the gate with an insider's story on a lame duck presidency that is already unpopular with the American public.

His book, What Happened — Inside the Bush White House and Washington's Culture of Deception, is due to be published next week, and the Washington Post and New York Times have run excerpts.

As press secretary, McClellan was the man in charge of explaining and defending White House policy to the media, and was referred to as the "Unanswer Man" by the Washington Post.

Now he is seeking to distance himself from that role, saying Bush was not "open and forthright on Iraq" and that he has bungled his role as a wartime leader.

"I still like and admire President Bush but he and his advisers confused the propaganda campaign with the high level of candour and honesty so fundamentally needed to build and then sustain public support during a time of war," McLellan writes.

"History appears poised to confirm what most Americans today have decided — that the decision to invade Iraq was a serious strategic blunder."

McClellan says he now believes the war "was not necessary" and top advisers, especially those "involved directly in national security," helped lead the president astray.

McLellan is critical of Bush himself for his inability to "change and grow" in the role of president.

Bush seemed unconcerned when the rationale for the war in Iraq — that Saddam had weapons of mass destruction — was shown to be fallacious, he writes.

Bush "convinces himself to believe what suits his needs at the moment," McClellan writes.

McClellan goes on to criticize the Bush administration's response of Hurricane Katrina in the 341-page book.

The White House "spent most of the first week in a state of denial," he writes and then-aide Karl Rove orchestrated a public relations disaster by having Bush survey the New Orleans disaster zone from the window of Air Force One.

"One of the worst disasters in our nation's history became one of the biggest disasters in Bush's presidency," he says.

McClellan resigned as press secretary in 2006.

Current White House aides seemed surprised by the scathing tone of the book, and Bush press secretary Dana Perino issued a statement critical of their former colleague.

"Scott, we now know, is disgruntled about his experience at the White House," she said. "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."

With files from the Associated Press