* Obama gets another chance after weak first debate
* Polls show race deadlocked with three weeks left
* Town hall format could change tone, strategy
President Barack Obama is under heavy pressure in his debate rematch with Mitt Romney on Tuesday to turn in a more forceful performance that restores his momentum and draws sharper policy differences with his Republican challenger.
Obama will try to make amends for his listless and heavily criticized showing in the first debate when the rivals square off in a nationally televised town hall setting that gives undecided voters in the audience the opportunity to question the candidates.
With just three weeks left in a deadlocked race for the White House, the Democratic president cannot afford to fumble another chance to make the case for his re-election and to blunt the rise of Romney.
"Almost all of the pressure will be on Obama this time, given how poorly he performed in the first debate and how much that seemed to help Romney and change the race," said Andrew Taylor, a political scientist at North Carolina State University.
"Obama has to steady the ship and instill confidence in Democrats again," he said.
Obama's passive performance in the Oct. 3 debate launched a Romney surge that now has the two candidates running virtually even in most national polls before the Nov. 6 election.
A Reuters/Ipsos online tracking poll on Monday showed Obama with a 2-point lead over Romney, 47 percent to 45 percent. That means they are essentially tied.
Obama and his campaign advisers have promised that a more engaged candidate will show up in the 90-minute debate at Hofstra University in New York, which begins at 9 p.m. EDT.
For Obama this time around, the challenge will be to confront Romney on the issues without seeming nasty or too personal.
Romney, a former private equity executive often accused of failing to connect with ordinary people, would be happy with a steady performance to keep up his momentum. Not only have his overall poll numbers improved since the last debate, but personal approval ratings have also crept up.
TOWN HALL FORMAT COULD CHANGE TONE
Both men will have to deal with the more intimate town hall format, which often inhibits political attacks as the candidates focus on connecting with the individual voters who ask the questions.
"It enables them to talk directly to people and look them in the eye and try to connect, which has not been a strength for either of them," Taylor said.
"But you can still make strong points with a velvet glove," he said. "You can make forceful points without seeming too harsh or antagonistic."
Obama was criticized after the last debate for failing to challenge Romney on his policies on taxes, healthcare and jobs, and particularly on what Democrats said were efforts by Romney to soft-pedal his most conservative stances.
Campaign aides said Obama was ready to take on Romney this time.
"You should expect that he's going to be firm, but respectful in correcting the record in the times we expect Mitt Romney will hide from and distort his own policies," said Obama campaign spokeswoman Jen Psaki.
Both sides have focused on new lines of attack since the last debate that are likely to come up on Tuesday. Romney has been on the offensive over the administration's handling of diplomatic security in Libya before the attacks there that killed the U.S. ambassador and three other Americans.
Democrats, hoping to make more inroads with women voters, have hit Romney and running mate Paul Ryan for their opposition to abortion rights.
Obama and Romney have taken time off the campaign trail to prepare for the showdown, the second of three presidential debates. The final one will be next Monday, Oct. 22, in Boca Raton, Florida, and will focus on foreign policy issues.