BOSTON (Reuters) - Mike Huckabee holds a small lead in the field of potential Republican presidential candidates, while Mitt Romney and Sarah Palin have slipped, according to a Gallup Poll released on Friday.

Gallup's survey of 1,000 Republicans and Republican-leaning independents taken on March 18-22 put support for former Arkansas Governor Huckabee at 19 percent.

Huckabee has been creeping up, from 18 percent last month, while backing for Romney has slipped from 16 percent in February and 19 percent in November. Palin, who held at 16 percent since September, dropped to 12 percent in the latest poll.

Gallup said its poll had a margin of error of plus or minus 4 percentage points.

Sixteen percent of Republicans currently have no preference in the upcoming contest for the Republican nomination for 2012, the poll said, and most leading contenders have not yet committed to run.

The presidential election is 18 months away, but there is widespread interest in who will face President Barack Obama, a Democrat. The first Republican primary elections to select their nominee will start in February.

Observers think Romney, now on a nationwide fund-raising swing, will almost certainly announce a second run for his party's nomination after falling short in 2008 to John McCain.

Prospects are less certain for Huckabee, a 2008 candidate who hosts a television show on Fox News.

Palin, who was McCain's running mate in 2008, also has a lucrative media career.

The poll also showed that if Huckabee does not run, Palin would be the most likely to pick up his supporters, and Huckabee would benefit if Palin does not run.

Newt Gingrich, former speaker of the U.S. House of Representatives, has said he could announce a run for the nomination in May. He ran fourth in the Gallup poll with 10 percent support, up slightly from 9 percent the previous month.

Former Minnesota Governor Tim Pawlenty on Monday announced an exploratory committee, the first high-profile Republican to show serious intent for 2012. He had 3 percent support in the Gallup poll, the same as a month ago.

Former U.S. Senator Rick Santorum and Mississippi Governor Haley Barbour, who will campaign in the key early-voting state of New Hampshire next week, each captured just 2 percent of potential voters in the poll. (Editing by Jerry Norton and Vicki Allen)

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