DES MOINES, Iowa (AP) — Former Massachusetts Gov. Mitt Romney was locked in a tight race with former Sen. Rick Santorum in Iowa’s Republican presidential caucuses, the opening contest in the campaign to pick a challenger to President Barack Obama.

Romney, the longtime front-runner, and Santorum, whose campaign only recently gained momentum, were separated by only 19 votes with nearly 90 percent of the state’s 1,774 precincts reporting.

Congressman Ron Paul was running a close third in the caucuses — evening meetings held at 809 locations across the midwestern state Tuesday.

Romney was looking for a strong performance in Iowa to strengthen his shaky front-runner status. Iowa is not considered a natural stronghold for Romney, so a solid showing there could boost his campaign going into next week’s New Hampshire primary, where he is the favorite.

Romney has cast himself as the most formidable potential rival to Obama, whose re-election prospects have been damaged by America’s sluggish economy. But Romney has struggled to win over conservatives. His support has hovered around 25 percent in what is now a seven-candidate field.

Almost all of his rivals have had brief surges in recent months, only to fade quickly under intense scrutiny. Santorum and Paul were the latest to rise in Iowa, though both are considered longshots to win the Republican nomination.

Santorum has long been at the bottom of Republican polls, but he has campaigned hard in Iowa, where his solid conservative stances on social issues like abortion and gay marriage resonate with the large numbers of evangelicals who dominate the state’s Republican base. It’s not clear whether the message will carry as well in more moderate states or if he can come up with the funds or organization to sustain a national campaign.

Paul’s advocacy of small-government, libertarian values has won him a devoted core of supporters, including in the important tea party movement which fueled the Republican wave victory in the 2010 congressional elections. But his anti-interventionist views and criticism of aid to Israel puts him at odds with much of the party.

Returns from 1,567 of 1,774 precincts showed both Santorum and Romney with 24.6 percent of the votes, while Paul had 21.1 percent. Santorum had 26,608 votes, Romney 26,589 and Paul 22,850.

Former House Speaker Newt Gingrich had 13 percent, followed by Texas Gov. Rick Perry, 10 percent, and Minnesota congresswoman Michele Bachmann with 5 percent. All three had, at some point in the campaign, been seen as Romney’s top rival.

Another candidate, former Utah Gov. Jon Huntsman, who served as Obama’s ambassador to China, is not competing in Iowa, choosing to focus on the New Hampshire primary.

Iowa has an uneven record when it comes to predicting national winners. It sent Obama on his way in 2008, but eventual Republican nominee John McCain finished a distant fourth here to former Arkansas Gov. Mike Huckabee. The 100,000 or so voters are disproportionately white and more conservative than the overall American electorate.

Still, a victory means a wave of publicity, a likely boost in campaign contributions and a guarantee of surviving for at least a few more contests. Candidates who do poorly may feel compelled to drop out of the race.

The caucuses’ importance was underscored by the estimated $13 million in television advertising by the candidates and their supporters.

Unlike in a primary, in which voting occurs over hours, the Iowa caucuses were meetings held in schools, churches and other locations where Republicans gathered for an evening of politics. Each presidential candidate was entitled to have a supporter deliver a speech on his or her behalf before straw ballots were taken.

Under party rules, caucus results have no control over the allocation of Iowa’s 25 delegates to the Republican National Convention in August, when the nominee is formally selected. The Associated Press uses the caucus outcome to calculate the number each candidate would win if his support remained unchanged in the pre-convention months.

Romney, who finished second in Iowa in 2008 despite a costly effort, initially campaigned cautiously this time around. But that changed in the race’s final days as he pursued a first-place finish, running as a conservative businessman with the skills to fix the economy.

The weak economy, though, was muted as an issue here. Despite areas of economic distress, the farm economy is strong. Iowa’s unemployment in November was 5.7 percent, sixth lowest in the country and well below the national reading of 8.6 percent.

Santorum, Gingrich, Perry and Bachmann argued that Romney wasn’t nearly conservative enough on the economy and social issues such as abortion.

Democrats watched carefully in a state that has swung between the two parties in recent presidential elections.

Obama was unopposed for his party’s nomination. Even so, his re-election campaign set up eight offices across Iowa, made hundreds of thousands of calls to voters and arranged a video conference with caucus night supporters.

“This time out is going to be in some ways more important than the first time,” Obama told Democrats across the state. “Change is never easy.”

The state’s leadoff spot has been a fixture for decades. Democrats moved the caucuses up to early January in 1972, and Republicans followed suit four years later.

Copyright 2012 The Associated Press.