President Bush and Democratic nominee John F. Kerry questioned each other's fitness to be commander in chief on Wednesday as the faraway war in Iraq echoed through the cornfields of north-central Iowa.

In dueling speeches 80 miles apart in this state, scene of one of the half-dozen closest contests in the presidential race, the candidates exchanged insults over the 19-month Iraq conflict, which has ousted Saddam Hussein but also provoked an insurrection and claimed the lives of more than 1,100 U.S. service members.

With 13 days before the election, Bush said Kerry has a "fundamental misunderstanding" of the fight in Iraq and is not capable of winning a war on terrorism. "The next commander in chief must lead us to victory in this war, and you cannot win a war when you don't believe you're fighting one," Bush said at a rally on the fairgrounds here where he suggested that the Democrat was unwilling to use military force.

Kerry, addressing his supporters in Waterloo, Iowa, said Bush was "in denial" about Iraq's problems. "The president says he's a leader," the Massachusetts senator said. "Well, Mr. President, look behind you. There's hardly anyone there. It's not leadership."

At stake in the exchange was a crucial distinction: whether Americans connect the unpopular war in Iraq with the more popular war against al Qaeda -- a perception that would benefit Bush -- or whether they see the two as separate or at cross-purposes, as Kerry has argued. Americans are split on the question, with 45 percent saying the Iraq war has helped the war against terrorism and 40 percent saying it has hurt, according to a poll released Wednesday by the Pew Research Center. Eight months ago, 62 percent thought the Iraq war helped the war on terrorism and 28 percent thought it hurt.

As part of that battle over perceptions, the candidates quarreled about the role of Abu Musab Zarqawi, who has emerged as a leader of anti-U.S. fighting in Iraq and is responsible for numerous kidnappings and beheadings of Americans. Noting that Zarqawi in recent days has pledged his fealty to Osama bin Laden and al Qaeda, Bush said: "If Zarqawi and his associates were not busy fighting American forces, does Senator Kerry think he would be leading a productive and useful life? Of course not. And that is why Iraq is no diversion but a central commitment in the war on terror."

Kerry agreed that Zarqawi is now an al Qaeda ally but blamed Bush for failing to deal with Zarqawi earlier. Kerry said the CIA found "no clear link" between Hussein and Zarqawi and said Bush could have removed Zarqawi before the war when he was in Kurdish-controlled northern Iraq. "We could have, but did not, take them out," Kerry charged. "That was a terrible mistake that this administration has never explained." The CIA regards the Jordanian-born Zarqawi as a local terrorist in Iraq who since the U.S.-led invasion of Iraq has become a terrorist figure of global significance almost on a par with bin Laden.

More broadly than the Zarqawi argument, each candidate accused his opponent on Wednesday of an inability to comprehend threats to the country. "If President Bush cannot recognize the problems in Iraq, he will not fix them. I do recognize them, and I'll fix them," Kerry thundered to a standing ovation. "I know it can be done . . . because chaos in Iraq is as bad for our allies and Iraq's neighbors as it is for us."

Bush, in turn, said Kerry "misunderstands our battle against insurgents and terrorists in Iraq" because he calls Iraq a "diversion" from the war on terrorism. The president also cited Kerry foreign policy adviser Richard C. Holbrooke, who said that "we're not in a war on terror in a literal sense" and calling it a "metaphor" such as the war on poverty. "Confusing food programs with terrorist killings reveals a fundamental misunderstanding of the war we face, and that is very dangerous thinking," Bush said.

As the candidates exchanged accusations about Iraq and terrorism, the two campaigns vied to keep the debate in the final days before the election on friendly turf: Bush questioning Kerry's ability to fight terrorists and Kerry raising doubts about Bush's handling of the Iraq war and domestic matters. In three days this week, the candidates have veered dramatically from security issues to domestic affairs and back.

Kerry adviser Michael McCurry said Wednesday's speech was probably the Massachusetts senator's last on foreign policy before the election. Kerry gave a glimpse at the strategy in his speech when he said Bush "wants to make it solely a contest about national security," but added: "I believe a president must be able to defend this country and fight for the middle class at the same time."

Kerry, rebutting Bush's criticism that he is weak on defense, ridiculed the president as a blustery leader who has weakened the United States. Kerry used the word "leader" or "leadership" at least a dozen times to talk about his skills and to deride the president's. Public opinion polls indicate that voters continue see Bush as a more decisive leader when it comes to the war on terrorism.

Kerry criticized the president for going to war with Iraq, not providing enough U.S. forces and equipment, and failing to build coalitions. "That's almost like a schoolyard decision," he said. "You learn more in elementary school and high school than they seem to have applied in the conduct of this war."

Kerry, joined on stage by a Sept. 11 widow and former CIA director Stansfield Turner, filled his speech with tough talk, saying Bush "took his eye off the terrorists" and pledging to double the Army's Special Forces into "the most versatile, deadly, anti-terrorist force the world has ever known."

Here in Mason City, Bush, on a daylong spin through Iowa, Minnesota and Wisconsin that was originally intended to highlight rural issues, again ridiculed Kerry for saying the Sept. 11, 2001, attacks "didn't change me much at all." Kerry had said that was because he already favored doing more to combat terrorism, but Bush asserted: "This unchanged worldview becomes obvious when he calls the war against terror primarily an intelligence and law enforcement operation."

Bush repeatedly characterized Kerry as naive about terrorists and hesitant to commit military force. "You cannot lead our nation to decisive victory on which the security of every American family depends if you do not see the true dangers of a post-September the 11th world," he said. "The war against terror requires all our resources, all our strength."

Keeping up the two-pronged nature of the campaign, Democratic vice presidential nominee John Edwards, on a trip through Ohio, sought to highlight his ticket's commitment to restoring jobs. "Just to be perfectly blunt about this, it is impossible for me to imagine the people of Ohio are going to vote to rehire a guy as their president that's cost them over 230,000 jobs," Edwards told workers in Canton. Several workers were employed by Timken Co., which Bush visited in 2003 to promote tax cuts. The company later announced plans to close three Canton-area plants that employ 1,300 workers.

Vice President Cheney, speaking at a diner outside Flint, Mich., sought to answer questions about lost jobs with an optimistic recounting of administration policies on tax cuts and education. "There's a lot being done. There's always more than needs to be done," Cheney said. Newsstands outside the Big Boy in Clio carried the day's sour local news. "Pontiac GM plant to lose 900 jobs," read the banner headline in the Detroit Free Press. "GM idles 900 here," read the Detroit News.

Inside, pastor Lonnie William Brown asked Cheney what he would do about "the jobs that are being shipped abroad." Cheney said that "about 111 million American taxpayers benefited from the changes we made in the tax code."

Of the battleground states, recent polls indicate that the closest are Florida, Iowa, Minnesota, New Mexico, Ohio, Pennsylvania and Wisconsin. From Iowa, Kerry flew to Pennsylvania and will visit Colorado, Nevada, New Mexico, Ohio and Wisconsin in the coming days. Bush will visit Florida, Ohio and Pennsylvania.

Romano was traveling with Kerry. Staff writers John Wagner, with Edwards, and Michael Laris, with Cheney, contributed to this report.

Shoring up his foreign policy credentials, Democratic presidential nominee John F. Kerry said "I do recognize" problems in Iraq and "I'll fix them."President Bush has assailed his opponent on the issue of using military force. "The war against terror requires all our resources, all our strength," he said.