The ad, dubbed “Think Independent,” was unveiled at King’s campaign headquarters, just days after Republican Charlie Summers launched his first TV ads. King’s ad will be airing in Portland, Bangor and Presque Isle, the campaign said.

Summers’ campaign said King was going on the airwaves sooner than planned after a battering series of attack ads from the U.S. Chamber of Commerce that dubbed him “King of spending.” But King said Friday that he planned all along to run ads after Labor Day and that he’s sticking to his promise to run a positive campaign.

He said he isn’t too worried by the negative attacks.

“I have real confidence in Maine people. They can see through that,” he said.

King, Summers and Democrat Cynthia Dill, along with three additional independents, are vying for the seat that’ll soon be vacated by Republican Sen. Olympia Snowe.

Using Google Earth technology, King’s ad zooms from an aerial view of the United States to the yard outside King’s home in Brunswick, where the former two-term governor says, “If you’re looking for someone who can get things done and shake up Washington, you’ve come to the right place.”

Lance Dutson, Summers’ campaign manager, sent an email to supporters on Friday titled “Running Scared” that suggested King was falling in the polls and playing catch-up. “We beat Cynthia Dill and Angus King to the airwaves, yet another sign of the momentum building around Charlie’s campaign,” he wrote.

Drew Brandewie, Summers’ spokesman, said Maine voters have a choice between “liberal Democrat Cynthia Dill, ambiguous Independent Angus King and a small business Conservative in Charlie Summers.”

Responding to questions, King said he’d watched portions of the Republican and Democratic conventions and felt confident in his endorsement of President Barack Obama for re-election. “If I had any doubts, Bill Clinton laid them to rest,” King joked.

Republicans have accused King, a former Democrat, of being a Democrat in independent’s clothing. King, meanwhile, has refused to say which party he would caucus with.

“I don’t agree with the president on everything. If I’m elected to the Senate and he’s the president, or if Romney is the president, I’ll vote with them when I think they’re right and I’ll vote against them when I think they’re wrong,” he said.

King’s campaign said the ad will be followed by another one next week. He declined to put an amount on the cost of the advertising other than to say it was less than the U.S. Chamber’s initial attack on him. That puts King’s purchase below $400,000.