AUGUSTA, Maine — A new poll shows independent Angus King holding a 26-point lead over his closest rival in the race for Maine’s open U.S. Senate seat, in contrast with other recent polls that have shown Maine’s Senate race to be closer.

King led the Senate race with support from 50 percent of respondents, according to a poll released Wednesday by Portland-based Pan Atlantic SMS Group. Republican Charlie Summers attracted the support of 24 percent of respondents while Democrat Cynthia Dill had 12 percent support. Some 14 percent were undecided.

Pan Atlantic surveyed 400 respondents by phone from Sept. 24-28, including only respondents who voted in Maine’s 2010 gubernatorial election and are likely to vote again on Nov. 6. The poll carries a 4.9 percent margin of error for most questions.

The Pan Atlantic survey offers a picture of the Maine Senate race that shows King with a wider lead than other September surveys showed.

A survey conducted by Rasmussen Reports on Sept. 25 found King with a 12-point lead over Summers, 45-33. Rasmussen surveyed 500 likely voters; its survey had a 4.5 percent margin of error.

Earlier in September, the Maine People’s Resource Center, which polled 856 registered voters, found King leading Summers 44-28 while North Carolina-based Public Policy Polling found an eight-point difference between King and Summers, 43-35, after surveying 804 likely voters. The Maine People’s Resource Center, which leans Democratic, conducted its poll Sept. 15-17 and had a 3.35 percent margin of error; Public Policy Polling surveyed respondents Sept. 17-18 and had a margin of error of 3.5 percent.

In a poll of 618 likely voters conducted by Portland-based Critical Insights, King was leading Summers 50-28. That poll, commissioned by the Portland Press Herald, was conducted Sept. 12-16 and carried a 4 percent margin of error.

The difference in poll results is likely a result of differing methodologies, said Pan Atlantic President Patrick Murphy. Pan Atlantic and Critical Insights use live interviewers while the other firms that have surveyed the Maine Senate race use automated telephone surveys.

“Some of these other polls are done like bullet polls,” Murphy said. “They don’t offer the opportunity for pollsters to pursue answers.”

Murphy said Pan Atlantic’s interviewers asked respondents only about King, Summers and Dill. They didn’t ask about independents Andrew Ian Dodge, Steve Woods or Danny Dalton.

The poll contained some promising numbers for supporters of same-sex marriage. Some 57 percent of respondents said they planned to vote for the state ballot measure that would legalize same-sex marriage in Maine while 39 percent were opposed and 4.5 percent undecided. Murphy, however, said the level of support in the poll was likely inflated, based on responses when Pan Atlantic asked respondents how they felt about same-sex marriage in general.

The survey also shows incumbent U.S. Reps. Mike Michaud and Chellie Pingree comfortably leading their Republican challengers in the state’s Second and First districts respectively, though the congressional surveys carried wider margins of error because of smaller sample sizes.

While Michaud led Republican Kevin Raye 52-32 in the Pan Atlantic poll, the survey carried a margin of error of 6.9 percent, meaning the results could vary by nearly seven percentage points. Pingree held a 57-24 edge over Republican Jon Courtney; that survey question carried a 7 percent margin of error.

The presidential results mirror those of other recent surveys, with 51 percent of respondents choosing President Barack Obama and 37 percent choosing former Massachusetts Gov. Mitt Romney. Some 10 percent of respondents were undecided.

Like other surveys, the Pan Atlantic poll found a narrower margin in Maine’s Second District, where Obama had a 49-38 edge over Romney, compared to a 53-35 edge in the First District.

Respondents were split on support for the Affordable Care Act, the Obama administration’s signature health care reform law. Forty-seven percent said they favored it compared to 41 percent who said they opposed it.

BDN political analyst Robert Long contributed to this report.