Washington • Most Democrats want to re-elect President Barack Obama, but one in five of his party’s supporters remain uncertain about keeping him in the White House, a new Salt Lake Tribune national poll shows.

The survey also reveals that 37 percent of likely U.S. voters — Republicans, Democrats and independents — want to give Obama four more years. The rest are split among a wide field of Republican contenders, led by former Massachusetts Gov. Mitt Romney at 17 percent and former House Speaker Newt Gingrich at 14 percent (the only GOP hopefuls in double digits).

Nearly a fifth of voters are undecided.

The survey, conducted Dec. 12-16 for The Tribune by Washington, D.C.-based Mason-Dixon Polling & Research, has a margin of error of plus or minus 3.1 percentage points.

“The poll reflects a great deal of uncertainty among voters about their options,” says Republican strategist Mark McKinnon, a former top adviser to 2008 GOP nominee John McCain. “The presidential contest is a long way from being settled.”

Republicans, just two weeks away from the Iowa caucuses, appear to be more engaged, with only 13 percent undecided. But there’s still a wide range of support among the GOP candidates.

Among GOP voters in the survey, Romney and Gingrich are in a statistical tie, 30 percent to 29 percent. A Washington Post-ABC News poll of Republicans, released Tuesday, also showed the two in a dead heat nationally, with each grabbing 30 percent.

Romney is the only Republican who fares well in a head-to-head showdown against Obama, with each garnering 47 percent of registered voters, according to a similar Post-ABC News poll. Obama has more than a 10-percentage point lead against Gingrich in a separate hypothetical matchup as polled by Rasmussen Reports this month.

In the Tribune poll, Texas Gov. Rick Perry takes 10 percent of the Republican vote followed by Rep. Michele Bachmann, R-Minn., at 7 percent and Rep. Ron Paul, R-Texas at 6 percent.

Former Utah Gov. Jon Huntsman trails at 1 percent among all U.S. voters and 1 percent among fellow Republicans.

Obama snags 33 percent of the nationwide independent vote, followed by 17 percent for Romney and 12 percent for Gingrich. Nearly a quarter of independents remain undecided.

Brad Coker, managing director of Mason-Dixon Polling & Research, notes that the combined Republican support far outweighs those who say they want to re-elect Obama, 45 percent to 37 percent. But 18 percent of all likely voters are unsure who they back, Coker says, showing that “a lot of people are not really thinking about this.”

The Tribune poll mirrors other national surveys, even though the question did not identify the possible candidates; voters were simply asked to name their pick.

Coker also points to the 13 percent of undecided GOP voters as evidence that “Republicans are tuned in. They are starting to take sides, and they know about the candidates.”

Obama garners 2 percent of the Republican vote, according to the poll, while Romney gains 5 percent and Gingrich 2 percent from Democrats.

The margins of error in the party results range from 5.2 percentage points to nearly 6 percentage points.