* Romney trails in polls, some show tightening
* Voters like Obama, but concerned about his performance
* Candidates spend day preparing, touring debate site
By Steve Holland and Sam Youngman
DENVER, Oct 3 (Reuters) - U.S. Republican candidate Mitt Romney gets his first chance on Wednesday evening to go head-to-head in a debate against President Barack Obama, and potentially turn the tide of a campaign that has seen him trailing for weeks.
The 90-minute encounter could reach 60 million people on television, a far bigger audience than watched either candidate speak at the Democratic and Republican conventions.
While that could pay dividends in attracting undecided voters, there is also the risk of a major mistake that could overshadow the last five weeks before the Nov. 6 election.
Both campaigns have been trying to tamp down expectations for their candidates' performance, but they kept up fierce attacks before the debate, and launched websites to provide instant responses during it.
Romney's campaign hammered the Democrats over Vice President Joe Biden's comment that the middle class has been "buried" for four years. Obama's team lashed back that Romney's team was resorting to a "desperate and out-of-context attack."
Running behind in the polls, Romney is more in need of a victory than Obama at the University of Denver, the first of three such face-offs scheduled in the next four weeks.
"I think (Romney's) got to have a pretty convincing win," said David Yepsen, director of the Paul Simon Public Policy Institute at Southern Illinois University. "He's had a bad few weeks and he needs to change the narrative of the campaign."
The debate will focus on domestic issues, which are particularly important as the U.S. economy struggles. I t will be moderated by Jim Lehrer of PBS and starts at 9 p.m. EDT (0100 GMT Thursday). Obama will get the first question and Romney the last word.
The two candidates spent the day in last-minute preparations. Romney met with his strategy team in the morning, before an early afternoon walk-through of the debate hall. His wife, Ann, was also attending the event.
Obama flew to Colorado from the resort in Nevada where he spent three days preparing. He toured the debate site as soon as he reached Denver, after Romney's visit, to get comfortable with the setting.
First lady Michelle Obama, who was campaigning in Reno, Nevada, also was to travel to Denver. Wednesday was the first couple's 20th wedding anniversary, but they delayed their celebratory dinner until Saturday.
Romney has been struggling for weeks to overcome the effects of a hidden-camera video of a private fundraiser in which he deemed 47 percent of voters to be Obama supporters dependent on government who do not take responsibility for their lives.
As voters have reacted to the tape and other Romney campaign stumbles, most polls show Obama maintaining a lead over the former Massachusetts governor, including in many of the battleground states, such as Ohio, Virginia and New Hampshire.
The Reuters/Ipsos daily tracking poll on Wednesday showed Obama up among likely voters by 47 percent to 41 percent. A new NPR poll showed Obama up 51 percent to 44 percent among likely voters.
A few other surveys showed a tightening race, including an NBC/Wall Street Journal poll released on Tuesday with Obama up by just 3 points among likely voters, at 49 percent to 46 percent. That compared with 5 points two weeks earlier.
In Denver, Romney must raise questions about Obama's handling of the U.S. economy and explain how his own plan would create more jobs and cut the budget deficit.
In a move that distracted from the economy theme, Romney supporters re-released a video late on Tuesday from a 2007 speech by Obama, then a senator, in which he criticized the government response to Hurricane Katrina, which devastated African-American areas of New Orleans.
Conservative media outlets said the tape showed the first black U.S. president trying to fuel racial fires. Others said the speech was widely reported at the time and called it a bid to deflect attention from policy before the debate.
Romney must get through the debate without losing his cool or appearing disrespectful to Obama, whom many Americans like despite his struggle to create jobs. The often robotic Republican could also do with showing some personality to make voters feel more comfortable with him.
"Americans who are thinking about voting for Romney need to hear from him about how he would change the country for the better," said Republican strategist Ron Bonjean. "They're leaning toward the devil they know, which is President Obama. Romney has to knock it out of the park by showing the contrast between himself and Obama."
The Democrat must tell Americans why they should consider themselves better off than four years ago, a key measure in every presidential election. He needs to explain what he would do to boost job creation in a second term.
With the U.S. jobless rate above 8 percent for 43 straight months, huge federal budget deficits, and increasingly expensive entitlement programs, the economy is voters' top concern.
The Obama camp notes that the president inherited a tough economy from his Republican predecessor, George W. Bush, and that things have improved, if slowly. His first term has been marked by fierce partisan battles that have frozen Washington into political gridlock.
Biden appeared to veer from that script when he told a rally on Tuesday that the middle class "has been buried the last four years," just longer than Obama's time in the White House.
Obama campaign aides later underscored that Biden was referring to the ill effects of Bush's policies, but Romney's team seized on what they called a "stunning admission." They hammered home the point with multiple news conference calls, a new ad and even an "Honest Joe" T-shirt, on sale for $30.
So far, voters have seemed willing to cede that Obama was dealt a bad hand, but they are looking for a clear way out of the economic doldrums.
"He's got to reassure people who like him that it's OK to vote for him again," Yepsen said.
While it is widely noted that Obama appears to have a lock on the likability quotient, he also has managed to win over voters on a broad array of issues.
A series of Reuters/Ipsos polls indicated that Obama had small leads on separate questions about which candidate would best handle the economy and who could create more jobs, even though Romney has made his business experience as the head of a private equity firm the centerpiece of his campaign.
Obama's campaign has cast Romney as a wealthy elitist who stashes his $250 million fortune in offshore accounts to avoid paying taxes, "flip-flops" his political positions depending on his audience and campaigns by attacking Obama rather than offering his own ideas for addressing the country's problems.
Obama himself has offered little in the way of a second-term agenda beyond more of the same policies.
Romney late on Tuesday provided a bit of detail on how he would achieve his pledge of giving taxpayers a sizable cut in income tax rates. He said in a Denver television interview he was considering capping tax deductions at $17,000 for most taxpayers as one way to pay for his plan.
The next two presidential debates are Oct. 16, in Hempstead, New York, and Oct. 22 in Boca Raton, Florida. B iden and Romney's running mate, U.S. Representative Paul Ryan, will debate once, on Oct. 11, in Danville, Kentucky.