ST. LOUIS — George W. Bush and John Kerry disagreed on the fundamental focus of the war on terror Friday night in a sharp second presidential debate.

Both candidates scored points essential to their case for the presidency, but neither dominated the issues or the forum enough to fundamentally change a tight race. Bush appeared more relaxed and engaged than he did in their first debate last week, and Kerry countered an image that he was stiff and distant in one-on-one exchanges with a studio audience.

Pollster Frank Luntz, who conducted a focus group Friday night of St. Louis residents who started leaning toward Kerry after last week's debate, said he believed that Kerry solidified gains he had made in the Miami debate.

Kerry did so, Luntz said, "by turning the debate on the war on terror to a debate on Iraq." But Luntz also said Bush scored by portraying Kerry as a flip-flopper and stressing the need to restrict medical liability lawsuits.

Still, it was Iraq that most divided the candidates.

Bush said the war in Iraq was central in the global war on terrorism.

"It is a fundamental misunderstanding to say that the war on terrorism is only Osama bin Laden," Bush said. "The war on terror is to make sure these terrorists don't end up with weapons of mass destruction."

Kerry, a senator from Massachusetts, said Bush's fixation on Iraq allowed nuclear arms threats in Iran and North Korea to grow unchecked.

The carefully controlled "town hall"-style event included an audience of 140 St. Louis area residents who told the Gallup Poll organization they were uncommitted to either candidate. They submitted questions in advance, and moderator Charles Gibson then chose the questions to ask.

For television viewers, the Washington University debate drew clear guns-and-butter differences.

Kerry portrayed himself as a more reasonable alternative to Bush, a more patient leader who would engage in "smart diplomacy" and rebuild international alliances. Bush said those were naive and dangerous instincts of a politician who would bow to political pressure, at home and abroad.

"I don't think you want a president who tries to become popular and does the wrong thing," Bush said. He invoked the late Ronald Reagan, whom Bush said risked popularity in Europe to confront the Soviet Union in the Cold War's final days.

The debate was campaign in the round, with Kerry and Bush each addressing questioners by their first names and roaming a bright red carpet. At one point, Kerry looked directly in the camera and promised not to raise taxes on anyone but the rich.