WASHINGTON -- In a conference room at the Democratic headquarters, President Barack Obama has been preparing for the debate next week, but the reviews of his staff are already in. Too long, they tell him. Cut that answer. Give crisper explanations. No one wants a professor; they want a president.

Hundreds of miles away in New England, Mitt Romney's team has been working to make sure he avoids coming off as a scold. His sparring partner, Sen. Rob Portman of Ohio, channeling Obama, has gone after him repeatedly, to the point of being nasty. The goal is to get Romney agitated and then teach him how to keep his composure, look presidential.

With more than 50 million people watching and the presidency at stake, the candidates will meet for their first debate on Wednesday at the University of Denver, and both are cramming like college students before an exam. But it is not enough to pore through the voluminous briefing books. Victory may come down to a single exchange, or a single impression, an answer that comes off as too edgy or, conversely, as too long-winded.

Obama's team records his practices to sharpen his responses so that they connect on a more visceral level with the television audience. One of Romney's aides calculated his words-per-minute rate in the primary-campaign debates to break him of the habit of feeling that he needs to rattle off the most statistics.

Romney's team has concluded that debates are about creating moments and has equipped him with a series of zingers that he has memorized and has been practicing on aides since August. His strategy includes luring the president into appearing smug or evasive about his responsibility for the economy.

Obama is not particularly fluid in sound bites, so his team is aiming for a workmanlike performance like his speech at the Democratic convention. He is looking to show that Romney would drive the country in an extreme ideological direction at odds with the interests of the middle class.

For both men, it is a chance to reintroduce themselves to the largest audience in the campaign to date. "The debate at one level is almost a Zen moment -- who is this person?" said Newt Gingrich, the former House speaker, who debated Romney during the Republican primary campaign. "What's the larger story? What are we watching? What's the drama we're watching?"

As the candidates prepare, the first trick for Obama is finding time. His rehearsals have started late and ended early because of events like the tumult in the Middle East. He showed up at one practice just after speaking at a ceremony for the four Americans killed in Libya, and aides found that his mind was elsewhere.

While advisers said Obama would present Romney as a dangerous alternative, the president has an incentive to avoid risks, given his lead in battleground states.

"The sale has been made," said Neera Tanden, who ran debate preparations for Hillary Rodham Clinton against Obama in 2008. "He just needs to reaffirm it. He just needs to not get in the way."

By contrast, Romney needs to change the dynamics of the race.

"The debates are very important," said Kevin Madden, a senior adviser to Romney. "We see it as an important opportunity to persuade those voters who haven't yet decided that Gov. Romney would take the country in a better direction."

Romney has focused on going after Obama without looking too aggressive. He participated in 23 debates during the nomination process, including a pair in Florida in which he effectively destroyed Gingrich's threat. But general election debates tend to be more sober than the food-fight-type confrontations of a primary season.

"He came in very, very aggressive, very well prepared and ready to stick with his pitch no matter what," Gingrich said. "That is a pretty good setup for Obama. The challenge he's going to have is he's essentially indicting Obama while standing next to him. He has to do it in a way that's firm, respectful and pleasant."

---