The first wave of televised political advertisements by an outside group attempting to influence the U.S. Senate race in Maine is expected to hit local screens today.

The U.S. Chamber of Commerce has bought what appears to be close to $200,000 in ads in Maine media markets, according to several public disclosure documents at local TV stations. The documents do not detail the content of the ads; however, the most likely target is Angus King, the independent former governor who enjoys front-runner status in recent polls.

If the cost estimate holds true, it will be the largest single campaign expenditure this year in a race that may help determine the balance of power in the U.S. Senate.

The purchase comes amid the chamber’s multi-state ad blitz targeting Democratic congressional candidates. While the content of the Maine ads are not yet known, many of the spots running in Florida, Montana, New Mexico, Ohio and Wisconsin attack Democratic congressional candidates. That trend may foreshadow a rough few days for King, whom Republicans have portrayed as a big-spending Democrat cloaked as an independent.

The Maine ads also follow the chamber’s endorsement of Republican candidate Charlie Summers, which was announced Wednesday. State Sen. Cynthia Dill is the Democratic candidate.

The chamber did not respond to a request for comment.

Public disclosure forms at WCSH Channel 6, the Portland-based NBC affiliate, show the chamber has paid $62,365 for 58 spots that will begin running tomorrow. Some of the spots run during prime time, such as the opening ceremonies of the Olympics — a spot that cost $6,000.

Records at WGME Channel 13, the local CBS affiliate, show 71 ad buys by the chamber totaling more than $42,000.

Advertising executives at WMTW Channel 8 told The Portland Press Herald that the chamber bought several spots totaling about $25,000.

The U.S. Chamber has vowed to become a major player during the 2012 election.

National campaign spending experts have predicted the organization will spend as much as $100 million trying to influence elections this year.

Campaign finance laws do not require the chamber, a nonprofit organization, to disclose its donors. That the organization can shield its donors has made it the target of transparency groups.

The chamber and other outside groups are advertising in a number of states to see whether the ads change the numbers in the race, said Anthony Corrado, a Colby College professor of government. If the ads work, he said, that attracts more money.

Corrado said the size of the initial ad purchases are somewhat conservative compared to a full-fledged effort to swing the elections. The chamber and other outside groups could spend millions of dollars in Maine if the race tightens, he said.

Corrado also said the chamber has become a major financial force in tight congressional races now that such nonprofits can spend unlimited money on political advertising without having to disclose where they get the money and how they spend it.

“What we know is that in each election cycle the chamber has spent more and more, (and) in 2010 the chamber was the No. 1 spender on television advertising among these outside groups,” Corrado said. “They have said they are going to spend even more this election cycle.”

Crystal Canney, spokeswoman for King, said Wednesday the campaign knew about the ad buy, which she described as “business as usual in Washington.”

“We’ve been expecting this,” Canney said. “The U.S. Chamber endorsement of Charlie Summers shows just how out of touch the organization is with Maine’s business community.”

Canney added that King had a strong record of having supported Maine businesses during his eight years as governor, including successful efforts to save jobs at Bath Iron Works with a shipbuilding tax credit program, luring National Semiconductor to Maine and creating the Maine International Trade Association.

King, in a separate comment, said, “Now I understand why Charlie Summers didn’t agree to keep super-PACs out of Maine,” a reference to King’s challenge to other candidates last month to participate in a plan to discourage spending by outside groups on the Senate race.

Federal election laws prohibit outside groups such as the chamber and so-called super-PACs from collaborating with individual campaign committees. However, campaign finance experts such as Corrado say the outside groups often have relationships with the candidates and follow the lead of the campaigns.

Lance Dutson, the campaign manager for Summers, said the ad buy showed that King’s record as governor makes him “extremely vulnerable to the issues that people care about now, which is jobs and the economy.”

Dutson added, “He managed the state in a way that was not fiscally responsible. Americans right, left and center understand that’s what we need right now.” Dutson said he had not seen the ads.

Dutson said King’s comparison of the chamber to a super-PAC was “ridiculous.”

“(The chamber) is the national representative of business and the free market today, and Charlie is proud to have received their endorsement,” he said.

Dutson added that the ad buy was a sign that King’s victory in November was not inevitable, adding that groups like the chamber wouldn’t make such a significant investment if Summers weren’t viable.

“I think this is one of many soon-to-come signs that this is a serious race,” Dutson said. “Free-marketers and business people want to keep this seat in Republican hands. And they see Charlie has a great chance to do it.”

Portland Press Herald writer John Richardson contributed to this report.