"Saddam Hussein is a threat," Kerry said. "He needed to be disarmed. We needed to go to the U.N. The president needed the authority to use force in order to be able to get him to do something, because he never did it without the threat of force. But we didn't need to rush to war without a plan to win the peace."
Later in the debate, the candidates shifted from Iraq, touching on other international challenges. They sparred most passionately about North Korea and its pursuit of nuclear weapons.
Bilateral talks on Korea
Kerry charged that Bush's decision to withdraw from bilateral talks with North Korean caused South Korea's president to leave Washington "bewildered" after a meeting with Bush. He called on the president to resume those talks.
Bush insisted that bilateral talks were the wrong strategy and that it was best to remain involved in broader talks that include China, South Korea and Japan.
Bush said bilateral negotiations would play directly into North Korean President Kim Jong Il's hand because they would mean he would be free of direct pressure from China and the other nations to halt his nuclear arms program.
Despite lingering anxiety and disillusionment among voters about Bush's handling of the Iraq war, and a steady stream of recent violence and bloodshed there, surveys show that voters are far more likely to trust the president to deal with Iraq than they are Kerry.
Kerry made an aggressive attempt last night to turn that tide against Bush, accusing the president of making the country less safe by opting to rush to war against Iraq rather than focusing on hunting down Osama bin Laden and battling terrorism.
Kerry sought to tie what he called Bush's foreign policy failures to domestic problems, faulting him for spending millions in Iraq that could be going to health care and education at home.
Bush allies said the president would seek to drive home to voters the message that he has been a consistent leader since the Sept. 11 terrorist attacks, even in the face of tough circumstances.
Rep. Ileana Ros-Lehtinen, a Florida Republican, said Bush was speaking not to the majority of either party, but to undecided voters - "that 10 percent that are in the middle, that we've got to reassure about the president's leadership."
"Even if you don't agree with his policies," Ros-Lehtinen said of the president, "he has been consistent."
The stark difference in style between Bush and Kerry was on clear display last night as the two faced off on the stage of the university's Convocation Center before an audience of about 600 and a television viewing audience of as many as 50 million.
PBS anchor Jim Lehrer moderated the debate, seated at a table facing Bush and Kerry.
The first debate took place in the hotly contested swing state of Florida, the site of the 2000 presidential recount, where Kerry plans to campaign through tomorrow morning, with appearances scheduled in Tampa, Kissimmee and Orlando.
Bush plans stops today in Pennsylvania, a battleground state he lost in 2000, and New Hampshire, which polls show is up for grabs despite being in Kerry's back yard. The president heads tomorrow for Ohio, another important state leaning in his favor.
Bush and Kerry meet next Oct. 8 at Washington University in St. Louis, Mo., a state that Kerry has all but ceded to the president, who is enjoying a substantial lead there in statewide polls.
That debate, a "town hall"-style forum where the candidates will be seated on stools before a smaller audience, could be an important chance for both men to smooth their rougher edges. For Bush, the St. Louis debate will provide a more intimate setting where the wartime president can showcase his folksy style. Kerry, who has long suffered from a reputation as cool and aloof, will have to show his human side.