MANCHESTER, New Hampshire (Reuters) - Republican presidential candidate Mitt Romney held a strong lead ahead of next week's race in New Hampshire, while Rick Santorum, who came out of the Iowa's contest nipping at his heels, was gaining ground, according to a survey released on Wednesday.

But Romney's closest rivals in the Granite State, Ron Paul and Jon Huntsman, lost ground with likely primary voters, the survey showed.

The morning after Romney's narrow victory in Iowa's caucus, the 7 News/Suffolk University daily tracking poll of voters showed the former governor of Massachusetts holding 43 percent support, level with his results over the last two days.

Texas Congressman Ron Paul trailed Romney by a widening margin, with 14 percent support among voters polled on January 2 and 3, down from 16 percent in results released a day earlier. New Hampshire primary voters will go to the polls on January 10 in the second contest of the campaign to choose a Republican rival to incumbent President Barack Obama in the November general election.

Santorum, the former Pennsylvania senator who trailed Romney by a narrow margin in Iowa's party caucuses on Tuesday, ranked fifth among New Hampshire voters with just 6 percent support. But the poll showed he had gained ground on former House Speaker Newt Gingrich, whose support level fell to 7 percent of respondents, down from 9 a day earlier.

"If Santorum surpasses Gingrich and knocks him into fifth place, it would be fatal for Gingrich," David Paleologos, director of Suffolk University Political Research Center, said in a statement.

Gingrich and Romney are expected to arrive in New Hampshire on Wednesday to continue their campaigning.

Former Utah Governor Jon Huntsman, who has focused his campaign on New Hampshire, held third place with 9 percent support.

The poll is based on phone interviews conducted on January 2 and 3 of 500 likely voters in the Republican primary and has a margin of error of 4.4 percent.

(Reporting by Scott Malone in Manchester, New Hampshire, additional reporting by Ros Krasny in Boston; Editing by Jackie Frank)

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