In their first, potentially decisive face-to-face encounter, President Bush and Sen. John F. Kerry last night clashed over Iraq, terrorism and who should be trusted to lead the nation in a dangerous world.

Alan Diaz, Associated Press Democratic presidential candidate Sen. John F. Kerry, left, and President Bush greet each other before the start of the presidential debate last night. Click photo for larger image. Related coverage Analysis: Four more years of the incumbent, or change? Around the U.S., voters try to decide Iraq and terrorist record stretched two ways in debate Politics puts marriages to the test Soros draws brickbats in anti-Bush kickoff Full text: Read the transcript of the debate

In a debate devoted to foreign policy, Kerry repeatedly argued that Bush had recklessly spurred the nation to war with Iraq with no clear plan for extricating U.S. troops. The result, he said, was a costly, strategic distraction from the continuing danger posed by Osama bin Laden's al-Qaida network and like-minded terrorists.

"This president has made, I regret to say, a colossal error of judgment. And judgment is what we look for in the president of the United States of America," Kerry said.

Bush dismissed Kerry's repeated criticisms and adamantly defended the war in Iraq, saying the world is safer because Saddam Hussein has been ousted from power. Bush argued that the fighting in Iraq and the battle against terrorism elsewhere were different fronts in the same war.

"My opponent wants you to forget that he voted to authorize the use of force and now says it's the wrong war at the wrong time at the wrong place," Bush said. "I don't see how you can lead this country to succeed in Iraq if you say 'wrong war, wrong time, wrong place.' What message does that send our troops? What message does that send to our allies? What message does that send the Iraqis?"

Kerry repeatedly said the president had placed too high a priority on Saddam Hussein at the expense of the fight against al-Qaida.

After Bush said, "The enemy attacked us," while justifying his decision to go to war in Iraq, Kerry responded, "The president just said something extraordinarily revealing and, frankly, very important in this debate. ... Saddam Hussein didn't attack us, Osama bin Laden attacked us. Al-Qaida attacked us."

Throughout the 90-minute debate, Kerry attempted to put the president on the defensive. He not only repeatedly criticized Bush's decision to invade Iraq and his conduct of the war, he also faulted the Bush administration's record on nuclear proliferation and for failing to slow potential nuclear arms programs in Iran and North Korea.

Bush appeared impatient with the constant critique, insisting that Kerry's attacks were at odds with the senator's own past positions and arguing that Kerry's statements disqualified him from being an effective commander-in-chief.

"We pursued al-Qaida wherever al-Qaida tried to hide. Seventy-five percent of known al-Qaida leaders have been brought to justice. The rest of them know we're after them," Bush said. "We've upheld the doctrine that said if you harbor a terrorist, you're equally as guilty as the terrorist."

At another point, Bush said, "The only thing consistent about my opponent is that he's inconsistent."

The often testy dialogue was leavened by a grace note near the end of the debate, when the candidates exchanged praise for one another's families.

"I admire Sen. Kerry's service to our country. I admire the fact that he is a great dad," Bush said. "I appreciate the fact that his daughters have been so kind to my daughters in what has been a pretty hard experience for, I guess, young girls, seeing their dads out there campaigning."

Kerry responded, "I appreciate enormously the personal comments the president just made.... And so I acknowledge that his daughters -- I've watched them. I've chuckled a few times at some of their comments."

"I'm trying to put a leash on them," a smiling Bush interrupted.

"Well, I know. I've learned not to do that," Kerry said. "And I have great respect and admiration for his wife. I think she's a terrific person...and a great First Lady."

The candidates agreed that the potential for terrorist groups to obtain nuclear weapons is the single most serious threat facing the United States. Kerry said the Bush administration has moved too slowly to control loose nuclear materials around the world, particularly in Russia. At one point Kerry noted that the Bush administration had secured less nuclear material in the two years since 9/11 than the United States did in the two years preceding 9/11.

Alyssa Cwanger, Post-Gazette Pulling for Kerry, from left, Faye George, from Duquesne; Jannie Marshman, from Lawrenceville; Dolores McCoy, from Sheraden; and George Hicks, from East Liberty, all members of Service Employees International Union, watch and listen at the United Steelworkers headquarters in Downtown Pittsburgh as President Bush makes a point. Click photo for larger image.

"We're going to get the job of containing all of that nuclear material in Russia done in four years," Kerry said. "And we're going to build the strongest international network to prevent nuclear proliferation."

Bush insisted that gaining control over those materials had been a top priority of his administration.

"My administration started what's called the Proliferation Security Initiative. Over 60 nations involved with disrupting the trans-shipment of information and/or weapons of mass destruction materials," he said.

Bush and Kerry disagreed sharply on diplomatic tactics to disarm North Korea. Kerry said Bush was mistaken in insisting on multilateral talks rather than dealing directly with the North Korean regime. Bush said Kerry's approach would be a fundamental error, leading to the collapse of the current six-nation talks in the region.

Both candidates expressed concern about recent moves by Russian President Vladimir Putin to assert increasing personal dominance over his nation. Bush, however, expressed more sympathy for Putin's role as an ally against terrorism.

"I don't think it's OK, and said so publicly," Bush said of Putin's seeming drift toward authoritarianism. "I think that there needs to be checks and balances in a democracy, and made that very clear that by consolidating power in the central government, he's sending a signal to the western world and United States that perhaps he doesn't believe in checks and balances, and I told him that."

Kerry said, "I regret what's happened in these past months. And I think it goes beyond just the response to terror. Mr. Putin now controls all the television stations. His political opposition is being put in jail."

Nonetheless, he added, "This is a very important country to us. We want a partnership."

Early in the debate, Bush side-stepped a question from moderator Jim Lehrer on whether the election of Kerry would increase the risk of a 9/11-type attack. But throughout the evening Bush repeatedly argued that Kerry's stance on Iraq made him unfit to be commander-in-chief. In a direct exchange about character, Bush said Kerry has not shown "certainty in his core beliefs."

"He changes positions on something as fundamental as what you believe in your core, in your heart of hearts, is right in Iraq," Bush said.

	Alyssa Cwanger, Post-Gazette Behind the president, Cristie Fowler, 26, and her husband, James Fowler, 24, from Ben Avon, join in the applause with other Bush supporters watching the debate at Finnigan's Wake on the North Side. Click photo for larger image.

"If America shows uncertainty or weakness in this decade," Bush said in his closing statement, "the world will drift toward tragedy. That's not going to happen, so long as I'm your president."

Kerry argued that certainty was sometimes a dangerous quality, noting that one could be "certain and be wrong."

"It's another to be certain and be right, or to be certain and be moving in the right direction, or be certain about a principle and then learn new facts and take those new facts and put them to use in order to change and get your policy right," he said. "What I worry about with the president is that he's not acknowledging what's on the ground, he's not acknowledging the realities of North Korea, he's not acknowledging the truth of the science of stem-cell research or of global warming and other issues."

The candidates' first face-to-face encounter came after weeks in which the consensus of polls had found Bush leading the race by a small margin. Bush appeared to have moved into the lead after the GOP convention at the beginning of last month.

After the airing of hundreds of millions of dollars of advertising by the two campaigns and allied groups, the debate afforded a chance for voters to assess the candidates in a relatively unfiltered environment. It was anticipated that as many as 50 million viewers tuned in for the 90-minute encounter.

Every sentence was minutely scrutinized by operatives for both sides who almost instantly filled the Internet and e-mail inboxes with a cascade of critiques of the opposing candidates answers.

That was the beginning of the war of spin that will continue for days in an attempt to mold voters' conclusions on what took place on the University of Miami stage.

The rules of the debate, staged by a bipartisan commission, restricted last night's encounter to the two major party candidates. Independent Ralph Nader courted media exposure outside the hall, but neither he nor any other third party candidate had reached the threshold of support in opinion polls needed to secure a place in the debate.

Last night's exchange opened a potentially decisive two-week period in which the presidential candidates and their running mates will meet four times. Bush and Kerry will travel to St. Louis next Friday, Oct. 8, for a session in which they answer pre-screened questions from a studio audience. Their series will wind up in Tempe, Ariz., on Oct 13 for a debate focused on domestic issues.

Vice President Dick Cheney and Sen. John Edwards will meet Tuesday for the sole vice-presidential debate at Case-Western Reserve University in Cleveland.

The atmosphere on the University of Miami campus was a festive contrast to the exhaustion and fear that Florida experienced in dealing with four hurricanes in the past month. Hundreds of Kerry and Bush supporting students, pumping signs for their candidate up and down, lined closed streets and gathered in grassy spots to cheer despite heavy security. Bomb squad trucks were parked ominously around the campus and squads of police officers on bicycles rode in packs around the palm-tree-lined streets. Chain link fences were erected around grassy knolls, but few students seemed to mind in the excitement of having both presidential candidates on their campus.