AUGUSTA, Maine — The contest surrounding a ballot measure that asks voters whether they favor legalizing same-sex marriage appears to be tightening, according to two new polls released Thursday that are the first public surveys on the subject since June.

In addition, one of the polls — conducted by the Portland-based Maine People’s Resource Center — shows incumbent U.S. Reps. Mike Michaud and Chellie Pingree with comfortable leads over the Republicans trying to unseat them.

The Maine People’s Resource Center and the North Carolina firm Public Policy Polling on Thursday released second rounds of polling data on the heels of results the firms released Wednesday that showed Angus King’s lead shrinking in the campaign for Maine’s open U.S. Senate seat.

The Maine People’s Resource Center — which is affiliated with the left-leaning Maine People’s Alliance, a statewide advocacy group — surveyed 856 registered Maine voters Sept. 15-17; its survey carries a 3.35 percent margin of error. Public Policy Polling — which was founded by Democratic pollster Dean Debnam — surveyed 804 likely Maine voters on Monday and Tuesday; its poll has a 3.5 percent margin of error.

The Maine People’s Resource Center found 53 percent of voters saying they would vote “yes” on a ballot question asking, “Do you want to allow the State of Maine to issue marriage licenses to same-sex couples?” Forty-three percent of respondents said they planned to vote “no,” while 4 percent of voters were undecided.

Public Policy Polling, which asked, “Question 1 would allow the State of Maine to issue marriage licenses to same-sex couples. If the election was today, would you vote yes or no on question 1?”, found 52 percent of voters saying they would vote yes, 44 percent no. Four percent of respondents said they were undecided.

Both polls show that the edge for same-sex marriage supporters has narrowed. The two surveys are the first to be conducted since Maine Secretary of State Charlie Summers — also the Republican candidate for Maine’s Senate seat — finalized the ballot question wording at the end of July.

A poll by the Portland firm Critical Insights conducted June 20-25 found a 57-35 edge for same-sex marriage supporters, and a survey conducted by the MassINC Polling Group for the Boston public radio station WBUR June 13-14 found 55 percent of voters supporting the same-sex marriage initiative, compared to 36 percent opposing it. The Critical Insights survey asked voters, “Do you want to allow same-sex couples to marry,” and the WBUR poll asked voters if they supported a law that would allow same-sex couples to marry and “protects religious freedom” by not requiring clergy to perform same-sex marriages.

“The poll that came out today continues to show strong majority support,” said David Farmer, spokesman for Mainers United for Marriage, the primary campaign leading the effort to legalize same-sex marriage.

Carroll Conley of Protect Marriage Maine, the primary campaign working against the same-sex marriage ballot measure, said polls have typically underreported the level of opposition to same-sex marriage.

“You see the underreporting of those opposed to it, and then you also see the heavy weight of undecideds going in the direction of traditional marriage or holding the status quo,” Conley said.

Public Policy Polling president Dean Debnam agreed that undecided voters tend ultimately to vote against same-sex marriage. “Despite the 8 point lead for passage this should be seen as a very close race,” he said in a statement.

In the congressional races, which were only polled by the Maine People’s Resource Center, Michaud led his 2nd District challenger, Kevin Raye, 56-37, while Pingree led challenger Jon Courtney 60-32 in the state’s 1st Congressional District.

The Michaud-Raye results were virtually unchanged from the Maine People’s Resource Center’s April survey, which found 53 percent of second district voters backing Michaud to 37 percent for Raye.

Those results contrast the last public survey sizing up that contest, which has been seen as potentially competitive by national Republican groups. The Portland firm Critical Insights found a closer contest when it polled voters in June. At that point, Michaud was leading Raye 47-35.

If poll results continue to show the race decidedly in Michaud’s column, it could determine the extent to which outside groups invest in the contest.

The closer results in June helped attract some support for Raye from outside Republican groups. The National Republican Congressional Committee elevated Raye to “Young Gun” status after the June poll, a label the committee reserves for candidates it sees as promising. More recently, Raye received the endorsement of the National Federation of Independent Businesses. And both he and Michaud have taken to the airwaves with television ads recently.

On Thursday, the Raye campaign announced it’s received the endorsement of the U.S. Chamber of Commerce. In Maine’s Senate race, the Chamber began a $400,000 ad campaign attacking frontrunner Angus King just days after announcing its support for Republican candidate Summers.

Michaud spokesman Dan Cashman called Thursday’s poll results “encouraging” while Kathie Summers-Grice, a consultant to Raye, said the poll oversampled Democratic voters, meaning the race is actually much closer.

“I think that’s, given the oversampled size, real good news [for Raye] and not very good news for Mike [Michaud],” she said.

Some 43 percent of resource center survey respondents identified themselves as Democrats, 32 percent as Republicans and 25 percent as independents. But that number reflects how people chose to identify themselves, not how they’re registered, said Mike Tipping of the Maine People’s Resource Center.

In November 2011, 33 percent of Maine voters were registered Democrats, 28 percent were registered Republican, and 36 percent were unenrolled, according to data from the secretary of state’s office.

Pollsters generally don’t weigh their results by party identification. “Most fundamentally, it is an attitude” that changes depending on outside circumstances, the Pew Research Center wrote on its website in August, “not a demographic.”

How voters identified their ideology is a more reliable measure, Tipping said. Some 44 percent of the survey’s respondents identified as “somewhat conservative” or “very conservative” compared to 35 percent as “somewhat liberal” or “very liberal” and 29 percent as moderate.

In the 1st Congressional District, Pingree’s 60-32 edge over Courtney also has changed little since the Maine People’s Resource Center’s April survey, when Pingree led Courtney 61-28.

Courtney has struggled to gain traction in his challenge against Pingree. His fundraising during the second quarter of 2012 amounted to about a tenth of what Pingree collected. He had $19,000 in campaign cash on hand as of June 30.

He also won the Republican nomination for the 1st Congressional District by a razor-thin margin over political newcomer Patrick Calder, and he has struggled to gain the attention of national Republican organizations like Raye has.

The Maine People’s Resource Center found job approval numbers for Gov. Paul LePage are virtually unchanged from the group’s last survey in April. The most recent poll found 39 percent of respondents approved of the Republican governor’s job performance, compared with 54 percent who didn’t approve. In April, 39 percent approved while 56 percent did not approve.

Watch for updates.