AUGUSTA, Maine — The first poll conducted since the March filing deadline for congressional candidates shows Republican Charlie Summers and Democrat Cynthia Dill holding early advantages in their U.S. Senate primary races.

The poll of 993 registered voters by the Maine People’s Resource Center was conducted from March 31 through April 2 and had an overall margin of error of 3.11 percent.

MPRC is affiliated with the Maine People’s Alliance, a progressive statewide advocacy group. The poll favored Democrats over Republicans 39 percent to 29 percent, with the rest of those polled unenrolled.

Summers, Maine’s secretary of state, had the most support among six GOP candidates who are vying to succeed U.S. Sen. Olympia Snowe.

Snowe, a three-term senator generally acknowledged to be a shoo-in, announced in March that she would not seek reelection, a move that prompted several Republicans to get into the race and several big-name Democrats to consider a challenge.

According to the MPRC poll, 27.6 percent of people surveyed said they would vote for Summers if the primary were held today. State Treasurer Bruce Poliquin, a former gubernatorial candidate, was next at 12 percent.

Former Maine Senate President Rick Bennett had 7.1. percent, followed by assistant Senate Majority Leader Debra Plowman at 5.7 percent. Small businessman Scott D’Amboise, the only GOP candidate who was in the race before Snowe dropped out, and Attorney General William Schneider were tied at 3.9 percent support.

However, 39.7 percent of those surveyed said they were undecided, a reflection that race is wide open. The margin of error for the GOP primary questions was higher, 5.5 percent, because the sample size was smaller.

University of Maine political scientist Mark Brewer said the poll doesn’t reveal too much because it’s still early.

“The numbers are all about name recognition at this point and that will change over the next several weeks,” he said. “For the Republicans, it will come down to how they distinguish themselves because a fair number will try to claim the conservative mantle.”

On the Democratic side, Dill had a slight edge in the four-way race with 20.3 percent, followed by former Secretary of State Matt Dunlap at 16.7 percent and state Rep. Jon Hinck at 6.2 percent. Portland home builder Benjamin Pollard had just 1.3 percent support.

Even more Democrats, 54.8 percent, were undecided, which could be a good sign for independent Angus King, the former two-term governor who many believe will get significant support from Democrats. The margin of error for the Democratic primary was 4.8 percent.

Brewer said he was surprised by Dill’s strong showing.

“I hadn’t considered that possibility; I thought Dunlap would sort of run away with [the nomination],” he said.

In a hypothetical match-up between King and the top Republican and Democrat, 56 percent of those polled said they would vote for King, followed by 21.8 percent for Summers and 12.2 for Dunlap. About 10 percent were undecided.

Brewer said King is clearly the favorite, but that doesn’t mean he’s a lock.

“If the Democrats nominate a candidate who can take 25 percent of vote, then maybe a Republican can win it with high 30s,” he said.

The MPRC poll also asked voters in Maine’s 1st and 2nd congressional districts who they support.

In the 1st District, incumbent Democrat Chellie Pingree leads Republican Jonathan Courtney, the current Senate majority leader, 61 percent to 28 percent with about 11 percent undecided.

“More and more, the 1st District is looking like a Democratic lock,” Brewer said.

In the 2nd District, incumbent Democrat Mike Michaud held a 53.1 percent to 36.7 percent advantage over Republican Kevin Raye, Maine’s Senate president, with 10.2 percent undecided.

“If I’m Michaud, I don’t love those numbers, but he is still ahead,” Brewer said.

Another poll question asked for an opinion on same-sex marriage, which will be the first question on the November ballot.

MPRC asked: “Do you strongly favor, somewhat favor, somewhat oppose or strongly oppose allowing same-sex couples to be legally married in Maine?”

More than 43 percent said they strongly favored legalizing same-sex marriage, while 14.5 percent said they were somewhat in favor. More than 28 percent were strongly opposed and 11.7 were somewhat opposed.

Follow BDN reporter Eric Russell on Twitter @BDNPolitics.