(AP) - Texas Rep. Ron Paul, former Massachusetts Gov. Mitt Romney and former Pennsylvania Sen. Rick Santorum vied for the lead Tuesday night in Iowa's remarkably close Republican presidential caucuses, opening night in the campaign to pick a challenger to President Barack Obama.

Early returns showed the three men separated by only a few dozen votes - even taking turns in first place as the evening wore on - a fitting conclusion for a race as jumbled as any since Iowa gained the lead-off position in presidential campaigns four decades ago.

The winner was in line for bragging rights - and perhaps much more - as the Republican nominating campaign makes the turn to primaries in New Hampshire on Jan. 10, then South Carolina and Florida before the end of January. For some of the also-rans, history suggested the first event of the year might also be the last.

The economy and the federal budget deficit were top issues, judged more important than abortion or health care, according to a survey of early caucus-goers.

About a third of those surveyed said they most wanted a candidate who could defeat Obama, and they tended to favor Romney. Paul held a broad advantage among the nearly one in four who called the selection of a true conservative their top priority, and he also made a strong showing among younger and first-time caucus-goers.

Supporters of the tea party made up about two-thirds of the electorate, and were nearly evenly split among Paul, Romney and Santorum.

The survey by Edison Media Research for The Associated Press and television networks was based on interviews with more than 700 people arriving at 40 precinct caucuses across the state.

Returns from 282 of 1,774 precincts showed Paul with 24 percent of the votes, and Romney and Santorum each with 23 percent.

Former House Speaker Newt Gingrich had 13 percent, followed by Texas Gov. Rick Perry, 10 percent, and Minnesota Rep. Michele Bachmann with 6 percent.

Obama was unopposed for the Democratic 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," the president told Democrats across the state. "Change is never easy."

The Iowa caucuses' outsized importance was underscored by the estimated $13 million in television advertising by the candidates and so-called super PACs as well as thousands of campaign stops designed to sway 100,000 or so voters.