As the first contest for U.S. Republican Party to pick its presidential nominee draws near, the candidates and volunteers began their final sprint Saturday just ahead of New Year holidays, toward the caucuses next week in Iowa.

Most of the GOP hopefuls spent their day holding campaign events across Iowa. Former senator from Pennsylvania Rick Santorum, whose poll numbers have been on the rise in recent days, took the stage at five community events statewide, while Newt Gingrich, former House speaker who has been sliding in polls, held two.

Other candidates kept themselves busy as well. Mitt Romney, the frontrunner, returned to the state during the day from New Hampshire, and Rick Perry, the Texas Governor, also held campaign events in the state.

Michele Bachmann, the Minnesota Congresswoman, spent her day in the state capital of Des Moines, having lunch with undecided voters and working the phone at her campaign's state headquarters to woo supporters for the caucuses on Tuesday night.

The only candidate who wasn't in the state was Ron Paul, the Texas Congressman who is basically tied in polls with Romney. He was spending the holiday back home with his wife. But his well-dressed army of young volunteers were working on the phone tirelessly at the campaign headquarters outside Des Moines, persuading voters to turn out to support the Libertarian lawmaker.

Volunteers in other campaigns also made a huge volume of phone calls, which is the most effective way to target voters in the sparsely populated state with only a few days left to the caucuses.

Ken Brolin, a volunteer who flew in from Richmond, Virginia, to support Gingrich, said he is working 16 hours a day, making 150 calls on average.

"I'll make phone calls, knock on doors, and talk to people, whatever it takes," said the 60-year-old Brolin.

Jordan Crandall, a volunteer from Oklahoma at Bachmann's office, said phone calls in the last few days are crucial for candidates.

"Phone calls will swing voters who haven't made up their mind," said a 21-year-old volunteer.

Crandall has a point. Polls have showed as many as 40 percent of the 120,000 people, who will participate in the Iowa caucuses, are undecided, and that provided the campaigns, especially those lagging behind, a path to victory.

The frontrunners are also facing some challenge. According to an NBC-Marist poll, Romney and Paul are running neck-to-neck, with Romney at 23 percent among likely caucus-goers and Paul at 21 percent. Meanwhile, Santorum has surged to the third place, from 6 percent last month to 15 percent. Gingrich fell from his lead of 28 percent to the fifth place at 13 percent. Perry was in the fourth place at 14 percent and Bachmann in the sixth at 6 percent.