WASHINGTON — Scott McClellan was the ultimate Bush loyalist. He went to work for President Bush when he was Texas governor in 1999, helped Mr. Bush gain the White House in 2000, and then came to Washington to defend the president for the next six years on such issues as the war in Iraq and Hurricane Katrina.

But Mr. McClellan’s explosive new book, which alleges that the Bush administration waged a “political propaganda campaign” in favor of the Iraq war and bungled the response to the storm that devastated the Gulf Coast, prompted a counterattack yesterday from some of his oldest political colleagues, who accused him of disloyalty and questioned his credibility.

The current White House press secretary, Dana Perino, said the president was “surprised” by Mr. McClellan’s assertions. “He is puzzled, and he doesn’t recognize this as the Scott McClellan that he hired and confided in and worked with for so many years,” Ms. Perino said, adding that Mr. Bush was “disappointed that if he had these concerns and these thoughts, he never came to him or anyone else on the staff.”

A former Bush political adviser, Karl Rove, compared Mr. McClellan to a “left-wing blogger,” and a former White House counselor, Dan Bartlett, told CNN it was “misguided for him to make these kind of broad accusations and draw these big conclusions about the president.”

Several former Bush administration officials have written tell-all accounts. In one book published this month, retired Army Lieutenant General Ricardo Sanchez accuses Mr. Bush and his top advisers of “gross incompetence and dereliction of duty” for their handling of the Iraq war.

But none was as close to Mr. Bush or his inner circle as Mr. McClellan, 40, an amiable Texas native who was widely known for his cautious demeanor. He started out in politics by managing several state election campaigns in the 1990s for his mother, who became Texas comptroller, and was recruited to the governor’s mansion by a Bush confidante, Karen Hughes.