ST LOUIS (Reuters) - Voters go to the polls across Missouri next Tuesday for a Republican presidential primary that costs $7 million to put on but has been labeled a mere "beauty contest" for the candidates because it is non-binding.
But the early contest, followed by a binding caucus due in mid-March, could serve as an indicator of momentum in the hard-fought campaign to determine who will face off against President Barack Obama in November.
"We think Missouri is up for grabs," Ryan Williams, a spokesman for Mitt Romney, said on Wednesday, adding that the former governor was determined to win on Tuesday. No plans for an appearance were immediately announced.
Former Pennsylvania Senator Rick Santorum on Monday became the first contestant to appear in Missouri, a swing state that narrowly supported John McCain in 2008.
Santorum, who received a rousing welcome from some 500 supporters at a community college in the St. Louis suburbs, said he saw the primary as an opportunity to send a message to Romney, the national front-runner.
Romney, a former Massachusetts governor, has been widely endorsed by leading Missouri state Republicans, but the selection of the state's 52 convention delegates is so arcane no one is making predictions.
The unusual primary situation emerged after Florida bumped up its primary to January 31, setting off a game of leap frog as various states including Missouri tried to increase their influence by moving ahead in the nominating process.
National Republicans thwarted the effort, stipulating that any state that held its contest before March 6, except those authorized to hold early votes, would see the size of its delegation slashed by half.
Missouri then moved its caucuses to mid-March to make the binding selections, leaving Tuesday as a statewide opinion poll.
"This is a very unique situation," state Republican Party spokesman John Prouty said. "It's very difficult to predict what will happen prior to the caucuses."
Several candidates who have already dropped out -- Herman Cain, Rick Perry and others -- remain on the Missouri ballot, while Newt Gingrich, who finished second in Florida on Tuesday, is not.
Even with no votes in the primary, Gingrich can fight for delegates during the caucus. Gingrich spokesman R.C. Hammond said the campaign would focus on the caucus in March when delegates would be awarded, rather than the primary on Tuesday.
With less than a week to go before the primary, Gingrich leads in a statewide Public Policy Poll, with 30 percent support over Romney's 27 percent and Santorum's 17 percent. Libertarian-leaning Congressman Ron Paul was trailing with 13 percent.
"Gingrich is making a very unwise move by blowing off Missouri," Romney's spokesman Williams said. "Governor Romney is making an investment for the future in the state and this shows he's truly running a national campaign."
Looking ahead to November, a survey released Thursday by Democratic pollster Public Policy Polling showed Obama tied with Romney in Missouri, and leading Paul, Santorum and Gingrich.
Romney and Obama drew 45 percent each in a head-to-head matchup, while Obama led Paul by 45-43 percent, Santorum by 47-44 percent and Gingrich by 49-42 percent in the poll.
Public Policy surveyed 582 Missouri voters January 27 to January 29 for the poll, which has a margin of error of plus or minus 4.1 percent.
Missouri Secretary of State Robin Carnahan, a Democrat, said the state was spending $7 million on the primary. Four years ago, Missouri's primary fell on "Super Tuesday" and 1.4 million people voted as each party saw a contested nomination race. Nearly 3 million voted in the general election.
Editing by Cynthia Johnston and Greg McCune