It would be "the height of irresponsibility" to pass the war along to the next commander in chief, she said Sunday.
"This was his decision to go to war with an ill-conceived plan and an incompetently executed strategy," the Democratic senator said in her first presidential campaign tour through the early-voting state of Iowa.
"We expect him to extricate our country from this before he leaves office" in January 2009, the former first lady said.
The White House condemned Clinton's comments as a partisan attack that undermines U.S. soldiers.
About 130,000 American troops are in Iraq, and Bush has announced this month he was sending 21,500 more as part of his new war strategy.
Pressed during a forum to defend her vote to authorize force in Iraq before the U.S.-led invasion in March 2003, Clinton responded by increasing her criticism of Bush.
"I am going to level with you, the president has said this is going to be left to his successor," Clinton said. "I think it is the height of irresponsibility and I really resent it."
Bush describes Iraq as the central front in the global fight against terrorism that began after the attacks of Sept. 11, 2001. "The war on terror will be a problem for the next president. Presidents after me will be confronting ... an enemy that would like to strike the United States again," he recently told USA Today newspaper.
One questioner asked Clinton if her track record showed she could stand up to "evil men" around the world.
"The question is, we face a lot of dangers in the world and, in the gentleman's words, we face a lot of evil men and what in my background equips me to deal with evil and bad men," Clinton said. She paused to gaze while the audience interrupted with about 30 seconds of laughter and applause.
Meeting later with reporters, she was pressed repeatedly to explain what she meant. She insisted it was a joke.
"I thought I was funny," Clinton said. "You guys keep telling me to lighten up, be funny. I get a little funny and now I'm being psychoanalyzed."
She told reporters that evil men included al-Qaida leader Osama bin Laden, who remains at large. "Isn't it about time we get serious about that?" she said.
During the town hall meeting, she tried to make clear that she thinks she would be a chief executive with enough fortitude to confront any danger facing the country, reports AP.
"I believe that a lot in my background and a lot in my public life shows the character and toughness that is required to be president," Clinton said. "It also shows that I want to get back to bringing the world around to support us again."
Clinton defended the role that Congress has played, saying newly empowered Democrats are beginning to build pressure on Bush to act, but the public needs to be patient.
"We are at the beginning of a process," Clinton said. "It's a frustrating process, our system is sometimes frustrating."