AMES, Iowa — After months of laying the groundwork, the first test of the Republican presidential candidates' viability is finally here.

Saturday's Iowa Straw Poll marks the first time Republican voters weigh in on the GOP presidential field with ballots and comes just as Gov. Rick Perry of Texas was to enter the campaign during a visit to another early nominating state.

The nonbinding results in Ames, Iowa, were likely to foreshadow the coming months here in the leadoff state.

"The Iowa Straw Poll is the first measurable proving ground for our Republican candidates for president," Republican Party of Iowa Chairman Matt Strawn said.

After that, just four months remain before the leadoff Iowa caucuses.

Mitt Romney leads national polls and many states' surveys for the chance to challenge President Barack Obama next fall. But there is no shortage of rivals looking to emerge as the top alternative to the former Massachusetts governor, who lost the GOP nomination in 2008.

The candidates with the most to lose were Minnesotans who were competing to fill the role of a Romney alternative: Gov. Tim Pawlenty and Rep. Michele Bachmann. The pair clashed during Thursday's debate in Ames: Bachmann said Pawlenty "sounds a lot like Barack Obama if you ask me"; Pawlenty said his rival posts "a record of misstating and making false statements."

Pawlenty, who has been languishing in early Iowa polls, is out to prove he's a strong player in the GOP race with a victory, while Bachmann hopes to build on momentum she's enjoyed since entering the race this summer.

"For some people, this is make or break," tea party activist Ryan Rhodes said.

Nine candidates are on the ballot in voting that runs for six hours during the daylong political festival on the campus of Iowa State University that doubles as a fundraiser for the Iowa GOP.

They include Romney, who won the straw poll four years ago but isn't actively competing this time, and former Utah Gov. John Huntsman, who has been bypassing Iowa almost entirely in his hunt for the nomination. Neither was scheduled to be in the state; both spent Friday in New Hampshire.

Perry and former Alaska Gov. Sarah Palin -- who made a splash Friday when she visited the state fair -- aren't on the ballot, but their supporters are waging write-in campaigns that could outpace candidates who have spent months trying to line up supporters to participate.

Others on the list, including former House Speaker Newt Gingrich of Georgia, Texas Rep. Ron Paul, former Pennsylvania Sen. Rick Santorum and businessman Herman Cain, hope for surprise showings.

"Part of it is whether the message resonates, but the bottom line is you better be pretty well organized," Iowa Christian Alliance head Steve Scheffler said.

On the Iowa State campus, a circus-like atmosphere was in the making, with campaigns putting up giant tents for live music and tangy barbecue to court activists. Between the entertainers, candidates had one last shot to pitch for votes.

Republicans wouldn't speculate how many people will spend $30 each to attend the event, but turnout in past has ranged from 14,000 to 23,000.

The straw poll has a mixed record of predicting the outcome of the precinct caucuses.

In the last election, Romney won the straw poll, but the big news was the surprising second-place showing of Mike Huckabee. Huckabee won the Iowa caucuses, but dropped from the race soon after. John McCain, who eventually won the nomination, didn't compete in the straw poll and finished in 10th place.

Poor showings usually force some candidates -- mostly those who are not well-known and are struggling to raise money -- to abandon their bids, and that could happen this year, too.

"What it is, is a winnowing process and that might happen to Pawlenty if he doesn't do well," said Republican strategist Rich Galen. "It sort of serves as a filter to clean out the candidates who probably shouldn't be there in the first place."