Social conservative Rick Santorum, former Massachusetts governor Mitt Romney, and anti-war advocate Ron Paul, are leading in caucus votes in the U.S. state of Iowa, in the first nominating contest of the 2012 presidential election.

With nearly half of the votes counted, Romney and Santorum are tied at 24 percent and Paul is slightly behind at 22 percent. But nearly half of Iowa voters said before the caucuses that they were still making up their minds, so the final outcome is difficult to predict.

The candidates have been furiously campaigning in Iowa, where residents braved the winter cold to cast their votes at party caucus meetings across the state Tuesday evening.

The Democratic Party also holds its caucuses. President Barack Obama is unopposed for the party nomination but hosted a live web chat with supporters in Iowa Tuesday night. He faces a difficult test to win another term in the November election. The nation's economy has recovered sluggishly from the 2007-2009 recession, leaving many voters questioning his leadership.

Campaigning for the Republican nomination, Paul, a U.S. representative from Texas, promoted his anti-war stance at a high school outside the state capital, Des Moines.

“There is no reason in the world that we cannot be strict constitutionalists, strong national defense and say that we should not send young people off to war unless it's absolutely necessary and necessary for our national security.”

At that same “Rock the Caucus” event, former Pennsylvania senator Rick Santorum encouraged students to hold their president and presidential candidates accountable.

“Every decision that's going to be made during the next few years, whether 'Obamacare' is repealed or whether it's kept in place, whether taxes are going to grow, whether this deficit that is now crushing the economy and will crush your pocketbooks in the future is going to be dealt with so you won't have a lower standard of living. Those are the issues.”

Minnesota Congresswoman Michele Bachmann said she is the one true core conservative in the race.

“Of all the candidates, I am the complete package, the one that's most in the image and likeness of a Ronald Reagan and Margaret Thatcher. That's what our country needs right now. That's what our candidate needs to be to take on Barack Obama, to beat him and make him a one-term president.”

Former House speaker Newt Gingrich told reporters that President Obama's health care reform is all wrong, and that the Massachusetts health care plan Romney supported as governor was a model for the policy.

“It's real easy. I said, we looked at it, we studied it, we concluded it was wrong. Unlike Romney, I've concluded it was wrong. He's still defending it. Nobody at the White House has said they relied on Gingrichcare to design Obamacare. They have said very clearly they relied on Romneycare. They actually had Romney staff in the White House helping design Obamacare.”

Voters in Iowa often do not pick the eventual presidential nominees for either the Republicans or Democrats. But the state's caucuses can push weak contenders out of the race, or propel stronger candidates to success in other states during the next several weeks.

Of the seven Republican contenders, one, the former U.S. ambassador to China Jon Huntsman, has not campaigned in Iowa. He is pinning his hopes on a good showing in the New Hampshire state primary January 10.