BOSTON (Reuters) - Massachusetts voters go to the polls on Tuesday to choose between a Republican newcomer and a veteran Democratic Congressman hoping to preserve the majority his party holds in the U.S. Senate.

Representative Edward Markey has enjoyed a strong lead in polls since launching his campaign six months ago to succeed fellow Democrat John Kerry, now U.S. Secretary of State. Markey's opponent is private equity executive and former Navy SEAL Gabriel Gomez, whose solid support among Republicans looks to be not enough to prevail in the liberal-leaning state.

Democrats currently enjoy a 54-46 majority over Republicans in the U.S. Senate and a win by Gomez could help the national Republican party in its bid to retake control in next year's midterm elections.

Gomez has run as an outsider, saying in campaign appearances that as a moderate voice he could help overcome partisan gridlock in Washington. Markey, meanwhile, has sought to tie him closely to the national Republican party, whose conservative positions on issues including gun rights and abortion restrictions do not play well with Massachusetts voters.

Both campaigns have closely studied the state's last special Senate election, three years ago, when previously little known Republican state lawmaker Scott Brown defeated the Massachusetts Democratic attorney general, Martha Coakley, to take the Senate seat the late liberal lion Edward Kennedy had held for 47 years.

Brown lost his re-election bid, in November, to Democrat Elizabeth Warren, a former Harvard professor.

A Suffolk University poll conducted June 19 through 22 showed Markey drawing support of 51 percent of 500 likely voters, with 41 percent of respondents backing Gomez.

Analysts have warned that likely low turnout in an off-cycle election could make for volatile results.

The seat is one of two in the U.S. Senate currently up for grabs. In October, New Jersey voters will select a successor to Democrat Frank Lautenberg, who died early this month.

New Jersey Governor Chris Christie named a Republican to hold Lautenberg's former seat until the special election, boosting his party's margin in the Senate by one vote.

(Editing by Dina Kyriakidou and David Gregorio)