Under attack for supporting America’s hard-line stance against Saddam Hussein, among other things, former Prime Minister Tony Blair considered announcing in the fall of 2002 that he would not seek a third term, his former spokesman said Monday. But Mr. Blair changed his mind and convinced his wavering cabinet the following spring that the impending invasion of Iraq was justified.

The revelation comes in “The Blair Years: Extracts from the Alastair Campbell Diaries,” a 757-page collection of diary entries written by Mr. Campbell, who served until 2003 as the former prime minister’s closest adviser, spin doctor, hand-holder and policy enforcer. Mr. Blair left office a few weeks ago, and by publishing now, Mr. Campbell — known for his combativeness and short temper on behalf of his former boss — says he is trying to ensure that his account of Mr. Blair’s early years in office is seen as immediate and authoritative.

The book will be published in the United States on July 31, by Knopf.