AUGUSTA, Maine — Charlie Summers’ Senate campaign and the Republican party’s Senate campaign arm are cheering the release of polling data this week that show independent former Gov. Angus King’s lead in the race for Maine’s open U.S. Senate seat tightening to a four-point advantage over Summers.

The poll, commissioned by the National Republican Senatorial Committee and released late Tuesday, shows support for King slipping, an uptick in support for Democratic candidate Cynthia Dill and no movement — positive or negative — for Summers, the Republican nominee.

Polling experts say it’s important to recognize the Republican group’s poll for what it is in evaluating the results. But even if its specific results differ from other recent surveys’, experts say it points to the reality that Maine’s Senate race has become a competitive one.

“Other polls are showing this race tightening up, too,” said Steve Koczela, president of Boston-based MassINC Polling Group, which conducted a public survey of the Senate race in mid-June after the Democratic and Republican primaries.

The National Republican Senatorial Committee on Tuesday released data from two polls it commissioned from Idaho-based GS Strategy Group. The first, conducted Sept. 5-6, showed King with 44.3 percent support and Summers with 33.5 percent. The second, conducted Sept. 24-25, showed King’s lead narrowing to 3.8 points. King had 37.3 percent support in that survey while Summers’ support level stayed at 33.5 percent.

Support for Dill jumped to 17 percent from 11 percent over the two surveys, while the undecided column grew to 12.3 percent from 11.3 percent.

The GOP senatorial committee has spent more than $940,000 on ads attacking King for his involvement in the wind energy business before he became a U.S. Senate candidate, according to expenditure reports filed with the Federal Election Commission.

“Partisan groups always have a reason for making their polling public,” Koczela said. “That’s the biggest thing to keep in mind. They’re not disclosing everything they do. They’re disclosing what they want to disclose.”

A memo accompanying the GS Strategy Group results said the firm surveyed 400 likely voters for each survey, and that the poll results carry a margin of error of 4.9 percent.

Independent pollsters adhering to professional standards would have provided more information about their methodology for surveying voters and weighting results, shared other questions they had asked and offered details on the demographic makeup of their sample, said Amy Fried, a political science professor at the University of Maine and a Bangor Daily News columnist and blogger.

“Those kinds of things can make a difference in the results that you get,” she said.

That’s not to say partisan groups’ internal polls aren’t reliable, Koczela said. The pollsters doing the surveys have their reputations to protect, he said.

But “partisan polls typically release the information that’s most beneficial to their candidate,” Koczela said. “It’s not that that information is wrong. It’s just that they didn’t release anything else.”

The internal polls that become public are only a portion of all internal polls. Largely for that reason, those polls tend to favor the candidate the sponsoring group supports by an average of six points, Nate Silver, who tracks polls for The New York Times’ FiveThirtyEight blog, wrote in 2010.

That’s why it’s important not to put too much stock in a single poll, Fried said.

“You have to look at the overall trends,” she said. “A single poll with this very tight margin right now is an outlier. Maybe if there were other polls done, it would show that it’s in line with other polls.”

The most recent public survey, conducted Sept. 25 by Rasmussen Reports, found King had a 12-point lead over Summers. King attracted the support of 45 percent of voters in that survey while Summers had 33 percent support and Dill had 14 percent.

About a week earlier, Public Policy Polling published a survey showing King with 43 percent support, Summers with 35 percent and Dill with 14 percent. And around that same time, the Maine People’s Resource Center published a survey showing King with 44 percent support, Summers with 28 percent and Dill with 15 percent.

The polling results make it clear that a key Republican strategy for winning the Senate race is to siphon Democratic support from King in hopes it will transfer to Dill, said Dan Demeritt, a Republican political consultant and former communications director for Gov. Paul LePage.

“It’s clear that the strategy is to bring Angus King back down to earth, and it’s working,” said Demeritt, who writes a column for the Maine Sunday Telegram. “The challenge for the Summers campaign will be climbing enough to catch Angus at his floor.

“The vote total of the independents will certainly be within the margin of victory one way or another, so they’re a factor,” he added, referring to independents Danny Dalton, Andrew Ian Dodge and Steve Woods.

Fried said these poll results could draw additional funds from outside Republican groups who might see the more than $2 million already invested by Republican forces having an impact. It also could inspire some Dill proponents to transfer their support back to King in hopes of preventing a Summers victory, she said.