Ms Plame said Mr McClellan's excerpt was "shocking"

In an excerpt from his book, Scott McClellan says George W Bush helped mislead the public over the role in the affair of two White House aides.

The CIA agent, Valerie Plame, says her identity was leaked because her diplomat husband opposed the Iraq war.

The White House said Mr Bush would not ask anyone to pass false information.

Lawsuit

Mr McClellan's book is not scheduled for publication until April and the excerpt released was brief.

It refers to a White House press conference he attended in 2003.

WHAT IS CIA LEAK CASE ABOUT? Libby was found guilty of lying to the FBI and a grand jury over revelations about CIA agent Valerie Plame's identity Critics said the White House leaked Ms Plame's identity to undermine her husband, ex-ambassador Joseph Wilson He had publicly cast doubt on the Bush administration's case for war in Iraq The alleged cover-up, rather than the leak itself, was the subject of the Libby trial

Q&A: CIA leak case

At the conference, Mr McClellan told journalists that the two aides Karl Rove and Lewis "Scooter" Libby were "not involved" in leaking Ms Plame's identity.

The excerpt reads: "There was one problem. It was not true.

"I had unknowingly passed along false information. And five of the highest ranking officials in the administration were involved in my doing so: Rove, Libby, the vice-president, the president's chief of staff, and the president himself."

Mr McClellan, who served as press secretary from 2003 to 2006, and his publisher later clarified the excerpt.

Peter Osnos of Public Affairs Books said Mr McClellan was not suggesting Mr Bush deliberately lied.

"He told him something that wasn't true, but the president didn't know it wasn't true," Mr Osnos said. "The president told him what he thought to be the case."

Libby, Vice-President Dick Cheney's former chief of staff, is the only person charged over the affair. He was sentenced to 30 months in jail for obstructing an inquiry into the leaking of the identity.

Lewis Libby is the only person to have been charged

However, Mr Bush intervened in July to prevent Libby from serving a prison term.

Ms Plame said Mr McClellan's excerpt was "shocking" and that she believed Mr McClellan had been "sent out to lie to the press corps".

Current White House press secretary Dana Perino said: "The president has not and would not ask his spokespeople to pass on false information."

In July a judge dismissed a civil lawsuit brought by Ms Plame against Mr Cheney and other Bush administration officials.

She maintained her cover had been blown after her husband, Joseph Wilson, a former ambassador, said the Bush administration had manipulated intelligence on Iraq to back its case for war.