DES MOINES, Iowa >> Seven Republican presidential contenders will try to use tonight’s debate in the leadoff caucus state of Iowa to cast themselves as the strongest alternative to one rival: front-runner Mitt Romney.

At least two — Rep. Michele Bachmann and former Gov. Tim Pawlenty, both of Minnesota — are hoping for a last-minute boost before an important weekend test vote that could make or break their campaigns. Former Utah Gov. Jon Huntsman is looking to make a strong impression in his first debate, while Texas Rep. Ron Paul is out to prove his ideas are more mainstream than fringe.

Others struggling to gain traction — former House Speaker Newt Gingrich, ex-Sen. Rick Santorum of Pennsylvania and businessman Herman Cain — are simply seeking to promote their issues and maybe even boost their profiles.

All risk being overshadowed by one Republican who won’t be on the stage — Texas Gov. Rick Perry, who has signaled he’s likely to join the field in the coming days and will visit the early nominating states of Iowa, New Hampshire and South Carolina this weekend.

“This is the official opening of the season,” said Republican strategist Terry Holt. “It’s the debut and you better have your best stuff ready. That raises the stakes.”

Romney, the former Massachusetts governor who lost the GOP nomination in 2008, is hoping for a repeat of a June debate in New Hampshire, where he emerged largely unscathed. He enjoys a commanding lead in fundraising and strong poll numbers and wants to protect both by sticking to his message.

“He will focus on jobs and why his 25 years of experience as a businessman and entrepreneur give him a unique set of skills to lead on the economy,” Romney spokeswoman Andrea Saul said.

It could be a winning strategy.

“For Gov. Romney, as the overall front-runner at this point, the key to any debate situation is to hold serve and continue to play to your strength, which is talking about the economy,” strategist Brian Jones said. “What’s been happening plays into the message of the Romney campaign.”

That was a reference to the recent debate in Washington over spending and a souring Wall Street, issues that have only emphasized the importance of the nation’s economy in the political debate. With unemployment stubbornly high and jobs not returning quickly enough, the Republicans are eager to go head-to-head with President Barack Obama in 2012.

His top rivals were determined to deny Romney that chance. Pawlenty, whose performance in a previous debate was panned when he initially refused to repeat the “Obamneycare” epithet he coined to link Romney’s health care law in Massachusetts with Obama’s national health overhaul, looked to repair his image and start anew.

“This is Pawlenty’s last chance,” GOP strategist Rich Galen said. “If he doesn’t do well, I suspect it’s three strikes and you’re out.”

Pawlenty knows he needs a strong showing if he’s to do well in the straw poll in Ames.

“The way forward for this country is going to start in Ames this Saturday,” Pawlenty told an audience in Atlantic, Iowa, on Wednesday. “It’s the end of the preseason in this campaign. This is the formal kickoff. I ask for your support. I need your help.”

He’s also hoping to deny Bachmann a triumph. During one interview, she was asked if she was a “flake.” Her first debate performance suggested she was not.

“I think that Bachmann has the most to gain and the most to lose. She is now a target where she wasn’t before,” former Republican Party of Iowa chairman Richard Schwarm said.

So, too, is Huntsman.

“The one who has the most to lose is Huntsman,” said Galen of Obama’s former ambassador to China. “A lot of people were hoping he would come on the scene and shake things up. There has been nothing.”

Huntsman aides said not to count him out.

“Jon Huntsman is going to demonstrate that he is the only leader who has a proven track record of conservative governance and job creation that the Republican nominee will need to beat President Obama next November,” spokesman Tim Miller said.

Yet in recent weeks, Huntsman has seen a raft of departures from his campaign, including his campaign manager.

That shake-up has paled in comparison to the one Gingrich suffered when his entire brain trust resigned earlier this year.

Laden with debt and having trouble raising money, Gingrich has severely curtailed his campaign schedule and is not participating in the straw poll. Santorum, too, has faced fundraising and polling troubles but has worked the grass-roots activists in Iowa to build support among social conservatives.

“Obviously the front-runner is Gov. Romney and he has got to maintain his position in the race,” Republican strategist Danny Diaz said. “The others will want to use this as a way to build some momentum.”