Story highlights The last major poll before Tuesday's Iowa caucuses is released

The poll shows Mitt Romney with 24% and Ron Paul with 22%

Rick Santorum takes third with 15%

Newt Gingrich, Rick Perry and Michele Bachmann follow

As Republican presidential candidates barnstormed through Iowa in the last few days before the first nominating contest of the 2012 Republican campaign, three rivals were trying to position themselves into a third-place finish behind the front-runners.

A Des Moines Register poll released Saturday night -- the last major poll before Tuesday's caucuses -- showed Mitt Romney and Ron Paul atop the field with 24% and 22% respectively.

Meanwhile, a surging Rick Santorum was at 15%, a sliding Newt Gingrich at 12% and Texas Gov. Rick Perry, who had surged to the top of the field before a series of gaffes and lackluster debate performances sent him tumbling, at 11%.

But if the last two days of the five-day sampling were considered separately, Santorum would rise to second place with 21% and Paul would fall to third with 18%.

Perry on Saturday continued to try to slow the former Pennsylvania senator's rise by attacking him on his record on earmark spending while he was in the U.S. Senate.

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"If you want to truly overhaul Washington, D.C., we can't do that with a senator who's voted to raise the debt ceiling eight different times allowing our debt to grow from $4.1 trillion (to) $9 trillion on his watch," Perry told a crowd in Boone.

"That's so much debt, it even exceeds what President Obama has done in the White House. And what is so important, I (have) got to ask Rick, what is so important that compelled to you to add greater debt to our children's charge card?"

Santorum responded by saying that it was his job as a senator to bring as much of Pennsylvania taxpayers' money back to his home state and that "Governor Perry hired people to go up to Washington D.C. and get money for Texas."

He said said Perry was trying to "rewrite history" and the abuse of appropriations came after he had left the Senate.

Gingrich's own rise in the polls last month after a series of strong debate performances was met with a barrage of negative ads by his rivals and political action committees supporting them.

The former House speaker got some positive reinforcement as the conservative publication Newsmax begins airing a half-hour special in the state promoting the candidate.

The "The Newsmax 2012 Election Special," hosted by Michael Reagan, son of former President Ronald Reagan, will air on "major broadcast outlets" throughout the weekend, according to the publication.

At a campaign stop in Council Bluffs, Gingrich tried to contrast his message with that of his rivals.

"We have positive ads about how to create jobs and how to balance the budget," he said. "And I feel like I can afford to be positive -- this may be a comment on our competitors -- I'm very comfortable being positive because starting with when I was a very junior congressman working with Ronald Reagan, we actually achieved positive things."

The Register poll was the latest to show former Massachusetts governor Romney and Texas congressman Paul at the top of the field. Despite making only eight trips to Iowa, Romney was at the top of CNN/Time/ORC International and NBC News/Marist polls released earlier this week with Paul close behind.

Polls indicate Romney is the overwhelming front-runner in New Hampshire, where the primary comes a week after Iowa.

Paul's rise to the top of the pack has come over the last couple weeks but most observers feel some of his views such as diplomacy instead of military action against potential threats like Iran are far outside the Republican mainstream and will keep him from winning the party's nomination.

Paul was spending the weekend in Texas with his wife but his campaign said he will be back on the trail Monday morning.

The congressman picked up an endorsement from a former -- and possibly future -- rival on Saturday when Gary Johnson, who dropped out of the Republican race last week to pursue the Libertarian nomination, urged his GOP followers to support Paul.

In his letter to supporters, Johnson, a former two-term governor of New Mexico, acknowledged his views and Paul's were not perfectly aligned.

"While Ron Paul and I are both libertarians, we don't necessarily agree on every single issue," Johnson wrote. "However, on the over-riding issues of restoring our economy by cutting out-of-control spending and the need to get back to Constitutional principles in our government, Ron Paul and I are in lock-step."

Romney started the day in New Hampshire, which holds its primary a week after Iowa, before returning to Iowa on Saturday.

Before departing New Hampshire, Romney told a crowd on the state's coast that Obama would be remembered as a "footnote in history," although he has already made history as the nation's first African-American president.

Perry's campaign is confident that its organization on the ground in Iowa will muscle aside Santorum and Gingrich for a third-place finish.

Minnesota Rep. Michele Bachmann of Minnesota, whose poll numbers remain in the single digits, is seeing smaller crowds at her campaign stops but predicted her barnstorming bus tour across the state will pay off on Tuesday.

"We had thousands of people flip and go my way," Bachmann said at a stop in Des Moines. "Probably no other candidate spent all their time going through Iowa. That's why we saw literally thousands of people flipping."

The other major Republican candidate, former Utah Gov. Jon Huntsman, is concentrating his efforts on the New Hampshire primary, which comes a week after Iowa.