A new poll suggests Republican Susan Collins is a strong favorite over Democrat Tom Allen in the race to retain her U.S. Senate seat.

The poll, conducted by SurveyUSA for WCSH 6, WLBZ 2 and the Bangor Daily News, found support for Collins at 55 percent and Allen, the 1st District congressman, at 39 percent if the election were held today.

The poll surveyed 675 likely Maine voters. It has a 3.8 percent margin of error.

Upon reviewing the numbers, a spokeswoman for Allen’s campaign said she believed they did not accurately reflect the tightness of the race.

“Reliable polling conducted internally shows this race to be very much in play and far closer than those margins,” Allen spokeswoman Carol Andrews said in a statement released Thursday.

“We are confident that the people of Maine want change and are beginning to realize that voting for Tom Allen is the way to begin solving our economic, health care and energy crises, to begin bringing our troops home from Iraq and to take care of our people here at home.”

The Collins camp welcomed the numbers, which her spokesman said demonstrated Mainers’ respect for the moderate lawmaker who has held the seat since 1996.

“It’s clear Maine people appreciate her hard work and aren’t swayed by negative and false ads that aim to distort her real record of accomplishment for our state,” Collins spokesman Kevin Kelley said.

The new poll comes as Allen’s campaign releases a television ad today highlighting the major differences between his record in the House and that of the incumbent senator.

The 30-second spot, “Big Differences” is set in a Lewiston town hall. In the ad, Allen stresses that the race with Collins isn’t personal, but “about old ideas or new ideas.”

The campaign has been a closely watched one, but the University of Maine’s Amy Fried said Allen’s attempts to draw distinctions between himself and Collins may be coming too late.

“They should have been drawing contrasts early on, instead of featuring the biographical ads for most of the summer,” Fried said, “It’s a little late to start defining your opponent now.”

Fried said the SurveyUSA results reinforced the long-held political notion that unseating an incumbent is a daunting task — even for another well-known and popular lawmaker.

Fried pointed to Collins’ high level of support among those who don’t identify with a political party or ideology as a particular problem for Allen.

Of those who said they were political moderates, 54 percent favored Collins. Forty-three percent favored Allen.

Independents, or those not enrolled in a political party, favored Collins 57 percent to 39 percent.

“We can’t say what people are thinking, but … it certainly means [Collins] is not seen as terribly conservative,” Fried said.

Collins did poll well among conservatives, and Allen polled strongly among liberals. Seventy-eight percent of conservatives favored Collins. Eighty-one percent of liberals favored Allen.

Also, 24 percent of Democrats favored Collins compared with 15 percent of Republicans who favored Allen.

Geography also had little impact on whom voters preferred. Collins led in both the north and south of the state by margins mirroring her overall lead, according to the poll.

Allen did fare better among abortion-rights voters with 52 percent favoring him and 45 percent Collins.

Collins held a lead among both men and women, although men were more supportive. Among men, she led Allen 59 percent to 38 percent with 3 percent undecided. Among women, the margin was tighter, at 51 percent to 40 percent with 8 percent undecided.