Clinton continues, "I thought I had acted in good faith and made the best decision I could with the information I had. And I wasn't alone in getting it wrong. But I still got it wrong. Plain and simple."
CBS News obtained an early copy of Clinton's book, not scheduled for release until next Tuesday, and published excerpts on its Web site Thursday afternoon. Clinton also writes about the Sept. 11, 2012, terror attacks in Benghazi, Libya, as well as the Obama administration's attempts to secure freedom for Sgt. Bowe Bergdahl, the Arab Spring, the Osama bin Laden raid and U.S. strategy in Afghanistan, Russia and Syria, according to CBS News.
Clinton's Iraq comments are significant considering how much her vote dogged her with the Democratic Party's antiwar activist base in the 2008 presidential primaries. Her chief rival, Barack Obama, opposed the Iraq war from the start; he gave a speech in 2002, when he was still an Illinois state senator, opposing military action in Iraq.
Throughout the campaign, Clinton struggled to strike the right tone rhetorically about Iraq and over time distanced herself from the vote, although she stopped short of saying she regretted casting it.
In a late 2006 interview on NBC's "Today" show, Clinton said, "Obviously, if we knew then what we know now, there wouldn't have been a vote." She added, "And I certainly wouldn't have voted that way."
A few months later, addressing a meeting of the Democratic National Committee, Clinton said, "If I had been president in October of 2002, I would not have started this war.... If we in Congress don't end this war before January 2009, as president, I will."
Clinton's language in "Hard Choices" is nearly identical to the language another 2008 Democratic primary rival, then-Sen. John Edwards (N.C.), used when he disavowed his vote to authorize military action in Iraq. Edwards began an op-ed about Iraq published in The Washington Post in 2005 with the sentence, "I was wrong."
Dan Balz contributed to this report.