Maine’s primary elections are still months away but the race for Sen. Olympia Snowe’s seat is already shaping up to be the liveliest contest for U.S. Senate in the state in more than a decade and a half.

There are now six candidates hoping to be the first person in more than 30 years to defeat Snowe at the ballot box, with the possibility of additional contenders entering the race before the mid-March qualification deadline.

The two Republicans, Scott D’Amboise of Lisbon Falls and Andrew Ian Dodge of Harpswell, have been running for a year or longer. Two new Democrats — Sen. Cynthia Dill of Cape Elizabeth and home builder Benjamin Pollard of Portland — recently joined Rep. Jon Hinck of Portland and former Secretary of State Matt Dunlap of Old Town on their party’s slate of would-be senators. Both parties will choose nominees on June 12.

If all six current challengers qualified for their respective ballots, the 2012 Senate race would feature the largest field of candidates since 1996 when Snowe’s Republican counterpart from Maine, Sen. Susan Collins, won her first term.

Snowe, a moderate Republican seeking her fourth term in the Senate, has substantial nationwide name recognition and a campaign war chest flush with $3.4 million and climbing, as of the end of December. She is also a formidable campaigner.

But several factors could make this Snowe’s most competitive race in years.

“It is going to be a much tougher road than she had six years ago,” said Jim Melcher, a political scientist at the University of Maine Farmington. “She is still going to have to sweat a little bit, but there is no question she is the favorite.”

For her part, Snowe already has a campaign office in South Portland and a staff of five headed by a veteran manager who has worked for some of the biggest names in the Senate GOP.

“She is taking nothing for granted,” Snowe campaign manager Justin Brasell said last week. “She is going to run an aggressive campaign and work to earn the support of Mainers again. She, of course, has a job to do [in Washington] and will continue to do that as well.”

A number of factors appear to be driving the surge in interest in Snowe’s seat.

D’Amboise, who announced his candidacy in early 2010, and Dodge are hoping to tap into sentiments among some Maine Republicans that Snowe is not fiscally conservative enough or who are still smarting over her support for President Obama’s stimulus package. Both men are also campaigning on issues of personal freedom, appealing to members of the tea party movement that helped usher Republican Gov. Paul LePage — a Snowe supporter — into the Blaine House.

D’Amboise has also traded sharp exchanges with Snowe over a lawsuit filed against Education Management Corp. because her husband, former Maine Gov. John McKernan, served as CEO and board chairman of the company.

Neither men has, to date, garnered a groundswell of support from GOP faithful. But D’Amboise pointed out on Sunday that his campaign has raised more than $500,000 so far — more than any previous Snowe challenger.

While he said he doesn’t expect to be able to match Snowe dollar-for-dollar, he believes people want a choice.

“We are out speaking about the fact that we need to get back to the conservative principles of the Republican party: fiscally conservative and morally conservative,” he said.

Melcher speculated that LePage’s early backing of Snowe may have discouraged other Republicans from entering the race. Democrats, meanwhile, perceive Snowe as moving to the political right to counter her primary challengers, which they hope could make her vulnerable among moderates and independents come November, he said.

Additionally, Democrats may be hoping to benefit from President Obama’s re-election campaign and the referendum on same-sex marriage, both of which may draw more young voters to the polls, Melcher said.

“But clearly Olympia Snowe is the favorite to win the primary and the favorite to win the general election,” he said.

Dunlap said at this point he is focused entirely on the June 12 primary, not the November election. But he believes that the struggling economy and discontent with Washington may be driving the unusually high interest among Democrats in challenging Snowe.

“People that I talked to — and a lot of them are independents or Republicans — are saying it is time for a change,” Dunlap said. “I think it is great, given how tough things are right now, that people are willing to step up” and run for office.

Mainers who plan to attend the coming regional party caucuses can expect to see the candidates or their representatives in attendance as they work to collect enough petition signatures to qualify for the ballot. And Brasell said Snowe plans to make caucus appearances all over the state as well.