The chairman of the independent commission investigating the 2001 terrorist attacks, former New Jersey Governor Tom Kean, had an ominous warning for the country as he released the panel's final report in Washington.

"Every expert with whom we spoke told us an attack of even greater magnitude is now possible, and even probable," he said. " We do not have the luxury of time. We must prepare and we must act."

Recent public opinion polls suggest the threat of terrorism is a prominent concern of voters this year and has been ever since the 9/11 attacks.

The polls also suggest the president's handling of the war on terrorism is his single biggest asset in his race with Senator Kerry.

" In a vast, free society such as ours, there is no such thing as perfect security," said Mr. Bush. "And no matter how good our defenses are, a determined enemy can still strike us. Terrorists only need to be right once. We need to be right every single time."

Senator Kerry has not shied away from the issue and his political ads on television emphasize his military experience in Vietnam and his foreign policy work in the Senate to bolster his credentials as a potential commander in chief.

The Massachusetts Democrat often mentions the security issue in his speeches even as he tries to highlight differences with President Bush.

" John Edwards and I would never think about sending young Americans, son and daughters, into harm's way anywhere in the world without telling the American people the truth," he said.

Terrorism, Iraq and the economy all figure to be major issues in this year's presidential campaign. But presidential historian Allan Lichtman of the American University here in Washington says the security issue is perhaps the number one concern of voters.

"The September 11 attacks, I think, define this campaign," he explained. "So much of what this president has been doing has been in response to September 11, including, in his view, the war in Iraq, homeland security and the Patriot Act."

Washington-based political analyst Stuart Rothenberg says the president's re-election prospects largely hinge on how Americans perceive his handling of both the war on terrorism and the situation in Iraq.

"I think if the voters evaluate George Bush generally on terrorism, I think it is an asset for him," he noted. "If the voters look specifically at Iraq, casualties and car bombs and things like that, then it is not nearly as good for the president."

Democrats say their challenge is to convince voters that Senator Kerry is up to the job of commander in chief and that he will vigorously pursue the war on terror.

Democratic strategist Celinda Lake says that process will begin with Senator Kerry's speech to the Democratic National Convention next Thursday.

"It is a time when our candidate really gets introduced on the stage by himself and I think people will see Kerry as a strong leader, a steady leader and they will get a better sense of him," said Ms. Lake.