CORAL GABLES, Fla. – Sen. John Kerry accused President Bush Thursday night of a “colossal error in judgment” in ordering the invasion of Iraq.

“The world is better off without Saddam Hussein,” the president shot back in campaign debate, adding his rival once said so himself. “I agree with him,” Bush jabbed at a rival he depicts as prone to flip-flops.

In a 90-minute debate dominated by a war that has claimed more than 1,000 American lives, Kerry called the conflict a diversion in the broader struggle against terror and the hunt for Osama bin Laden.

The four-term Massachusetts senator said he could do a better job than Bush of protecting the nation against another Sept. 11-style attack, and pledged to be strong and resolute in fighting terrorism.

“But we also have to be smart … and smart means not diverting our attention from the war on terror and taking it off to Iraq,” Kerry said.

“This president, I don’t know if he really sees what’s happening over there,” Kerry said of Bush, standing 10 feet away on a University of Miami debate stage.

Bush swiftly returned to his theme of Kerry as a man who changes his mind too often to be president.

“He voted to authorize the use of force and now says it’s the wrong war at the wrong time. …. I don’t think you can lead if you say wrong war, wrong time, wrong place. What message does that send to our troops?” said the Republican incumbent.

With less than four weeks until the election, the polls show Bush with a small lead in the race for the White House, and several battleground states exceedingly close. Even some Democrats said the debate, with a national television audience in the tens of millions, represented Kerry’s best chance to gain late-campaign momentum.

Both men used well-rehearsed lines during their face-to-face encounter, but this was the first time each had to listen to the criticism at close quarters.

Bush appeared perturbed when Kerry leveled some of his charges, scowling at times and looking away in apparent disgust at others. Kerry often took notes when the president spoke. Some networks offered a split screen to viewers so they could see both men at the same time and watch their reactions.

Bush and Kerry differed over North Korea, Iran and Russia as well as Iraq in a debate limited to foreign policy and terrorism.

Kerry charged that North Korea and Iran both have advanced their nuclear weapons programs during the Bush administration.

“As president I’ll never take my eye off that ball,” the senator said.

Bush said he believed that a diplomatic initiative currently under way could solve the crisis with North Korea.

“On Iran, I hope we can do the same,” the president said.

Bush said that with North Korea, he would continue to pursue a strategy that involves the United States, China, Japan, Russia and South Korea in talks with North Korea to defuse the crisis. Kerry advocated bilateral talks between the United States and North Korea to find a solution.

Kerry voiced concerns about conditions in Russia, saying that crackdowns initiated by Vladimir Putin go beyond what’s necessary to combat terror.

Bush said he had a good personal relationship with Putin that “enables me to better comment to him and the better to discuss with him some of the decisions he makes.” Bush said Russia was a country in transition and that would remind Putin “of the great benefits of democracy.”

Not long before Bush and Kerry strode on stage, U.S. and Iraqi forces launched a major attack against insurgents in Samarra. The U.S. command said government and police buildings had been secured in the city.

The two men clashed time and again over Iraq and the broader war on terror.

Kerry said he had a four-part plan to battle terrorists, and said Bush’s could be summed up in four words – “More of the same.”

“You cannot lead the war on terror if you keep changing positions on the war on terror,” retorted the president.

Kerry appeared to taunt the commander in chief at one point during the debate when he said his father, former President George H.W. Bush, had stopped troops from advancing on Baghdad after they had liberated Kuwait during the 1991 Persian Gulf War.

Now, he said, the son ordered an invasion of Iraq anyway, without an exit strategy, and under conditions that mean the United States has incurred “90 percent of the casualties and 90 percent of the cost.”

In response, Bush ridiculed his opponent, saying he denigrated U.S. allies in the war, voted against an $87 billion measure to aid Afghanistan and Iraq and sent mixed signals.

“What’s his message going to be? Please join us in Iraq for a grand diversion?” Bush said to Kerry’s contention that he could summon broader international support for the war. “They’re not going to follow someone whose core convictions keep changing because of politics.”

In response to one question, Kerry said Bush had misled the country on the war by pledging to plan carefully, give diplomacy every chance to prevail and more. He said bin Laden, the al-Qaida leader responsible for the Sept. 11 terrorist attacks, had used the invasion as a recruiting tool for terrorists.

Bush said that was an “amazing claim,” and said the United States, not bin Laden, should decide America’s strategy in the war on terror.

Again, he said Kerry had changed his mind on the war, but this time, Kerry insisted that he had held one consistent position.

“The only thing consistent about my opponent’s position is he’s been inconsistent,” Bush said.

Members of Maine’s Congressional delegation scored the debate along party lines.

“President Bush clearly and decisively set forth his vision for America,” said Republican Sen. Susan Collins. “He left no doubt about where he stands and showed us why he is the right person to lead America for the next four years.”

Rep. Tom Allen, a Democrat, said Kerry showed greater command of the issues than the president.

“Sen. Kerry’s positions were much more thoughtful and clearer than what the president was saying,” Allen said.

Given the stakes, it was not surprising that the two campaigns negotiated what amounted to a 32-page contract that covered debate details. They ranged from the choice of moderator (Jim Lehrer of PBS) to the distance between the candidate lecterns (10 feet).

Even so, a last-minute controversy flared, as Kerry’s aides objected to the placement of timing lights on the lecterns.