President Bush and Democratic challenger John F. Kerry returned to the campaign trail Friday and resumed the intense dispute over the Iraq war and homeland security that dominated the first presidential debate Thursday night.

After Kerry's strong performance in the showdown in Coral Gables, Fla., appeared to boost his candidacy, the two candidates pounced on remarks made during the lively foreign policy debate to open new lines of attacks and buttress old ones during campaign appearances in battleground states. Kerry said the administration has failed to sufficiently secure the United States from future attacks, while Bush accused his challenger of undermining U.S. troops in Iraq.

As both campaigns struggled to determine how the widely watched debate had altered the race, Kerry told supporters at the University of South Florida that the president was resorting to Orwellian tactics to conceal the administration's failure to track terrorism suspects and prevent another strike on U.S. soil. Seizing on a new report that the government has not compiled a viable, unified terrorist watch list, Kerry said that "it's a complete failure, yet this president stands there and pretends to America that we're doing all that we can."

Bush, trying to fight back after what even some Republicans called a lackluster debate performance, said Kerry proved in their first encounter that he lacks the clarity and consistency to triumph in Iraq, as well as the resolve to protect the United States without first getting the approval of other nations.

"Senator Kerry last night said that America has to pass some sort of 'global test' before we can use American troops to defend ourselves," Bush said in Allentown, Pa., before delivering a similar message in New Hampshire. "The use of troops to defend America must never be subject to a veto by countries like France."

It is too soon to determine whether Kerry has erased what both sides considered the president's narrow lead heading into the debate. But Republicans and Democrats alike agreed that Kerry enhanced his chances of winning in November by hammering the president's credibility on Iraq and avoiding the meandering responses that have plagued him throughout the campaign. Some conservatives, such as Kate O'Beirne of the National Review, said Bush's performance was damaging. "I thought the president was repetitive and reactive," she said.

Privately, some Bush aides reacted grimly to his showing and made few of the usual post-debate proclamations that their man had won the exchange. In an e-mail to reporters, the normally boastful Bush campaign suggested that the debate was a tie.

At the same time, Kerry appeared as confident as he did after the Democratic National Convention in July, hugging aides and advisers, who strained not to gloat. If nothing else, Democrats -- including some Kerry aides who had become concerned that the Massachusetts senator was on the verge of losing the race -- sounded reenergized -- and relieved.

Michael McCurry, a senior Kerry adviser, predicted that the polls, which show Bush with a single-digit lead, will not change noticeably in the immediate days ahead. But he said Kerry successfully set the stage for the next two debates, which will focus on domestic policy. "We believe people are taking a new, fresh look, and that's a very important achievement for us in the debate," he said.

Kerry's camp said Bush's biggest substantive blunder was suggesting that the country could not afford new homeland security measures. "I don't think we want to get to how he's going to pay for all these promises," Bush said. "It's like a huge tax gap."

Kerry shot back Friday: "My friends, this is the president who created a tax gap by providing a tax cut to the wealthiest Americans instead of investing in homeland security in the United States. Let's get real." Bush has increased spending on homeland security; Kerry says he would spend more.

McCurry said the president's biggest mistake in the debate was, perhaps, more stylistic. "It looked like there was nowhere else in the world that he did not want to be," he said. News shows on Friday replayed images of the president scowling and appearing uneasy.

The president and his aides sought to highlight an apparent contradiction in Kerry's arguments Thursday night.

Bush noted that Kerry asserted that the war in Iraq is a mistake, then said that he did not believe U.S. troops in Iraq are "dying for a mistake," as the senator had said of the Vietnam War.

Milbank is traveling with Bush. Staff writer Matthew Mosk, traveling with Edwards, contributed to this report.