WASHINGTON - The magnetic Montana Senate race has attracted hundreds of thousands of dollars worth of TV ads produced and paid for by outside national groups seeking to influence the judgment of state voters.

While Sen. Conrad Burns, R-Mont., his Democratic challenger Jon Tester and the two parties have blanketed the airwaves with their messages, some outside groups - many based in Washington, D.C. - have also stepped into the state with their own ads.

With voters unlikely to know where the groups are based and who funds them, the groups have run ads labeling Tester a big taxer and attacking Burns for ties to Big Oil.

One ad currently on the air was paid for by the Free Enterprise Fund Committee, a tax-exempt advocacy group known as a "527" for its status under the tax code, said spokesman Todd Schorle.

The ad has been running for more than a week and the group plans to continue running it all this week and next, Schorle said. The group may run a different ad in a couple weeks, likely staying on the air in Montana very close to the elections in early November, he added.

The Free Enterprise Fund Committee ad titled "Paint Job" accuses Tester of wanting to paint over his record and to raise taxes if elected, concluding, "Tell Jon Tester you can't afford higher taxes."

The Washington, D.C.-based group formed just last month, and in its initial report to the IRS stated the purpose of its organization as "education and issue advocacy regarding the free enterprise system and pro-growth, free-market economic principles."

The group is connected to the Free Enterprise Fund, a nonprofit conservative think tank. According to a report filed with the Federal Election Commission, the Free Enterprise Fund in early October spent almost $125,000 on television ads targeting Tester in the Montana Senate race.

Schorle said the ad is part of a broader campaign by the group. It has already run different ads in Connecticut and Virginia and plans to do so in Tennessee, New Jersey and Illinois.

"We're up there basically trying to inform the people in Montana and in that district on Jon Tester's stance on taxes," Schorle said. "He basically is trying to cover up that he's a higher taxer."

But he added that the group's main goal is to make sure economic issues stay alive now. "We're not trying to swing voters, we're just trying to inform them on issues," he said. "Sometimes issues get lost in elections."

Campaign Money Watch, a project of the Public Campaign Action Fund, ran ads punctuated with the sound of a cash register showing an "oil executive" holding a cigar and saying that Burns voted for billions in tax breaks and subsidies for the oil companies.

The ad ran for the last two weeks of September and is no longer on the air. The Washington, D.C.-based 527 group spent roughly $100,000 airing the ad, said David Donnelly, director of Campaign Money Watch.

The group doesn't plan to run any more ads in Montana, but has run a similar ad in Ohio and may run similar spots in other states, he said. Campaign Money Watch works to hold candidates accountable for the money they raise and the positions they take in support of their donors, he said.

Public Campaign Action Fund works to improve campaign finance laws.

Donnelly said the group chose Montana to run ads because of oil and gas companies' contributions to Burns, his votes on energy issues and his ties to the Jack Abramoff lobbying scandal.

"It's a race in a state where a lot of interest is focused on money in politics and corruption," he said.

Americans United, a labor-backed group with Democratic ties, ran an ad about high gas prices that did not mention Burns by name but said it's time for a change, adding, "Tell George Bush and his backers in Congress we want a new direction."

The Washington, D.C.-based group spent almost $53,000 to air the ad in Missoula and more than $46,000 to air it in Billings from Aug. 25 to Sept. 7, according to the group.

Press secretary Jeremy Funk said the ad was directed towards Burns because he has taken contributions from gas and oil companies over the years.

Some groups run ads for just a short time. VoteVets.org ran an ad statewide during the last weekend of September featuring an Army reservist who served in Iraq in 2003 firing at two vests, only one of which stops his bullets. He accuses Burns of voting against giving U.S. troops modern body armor.

According to a report filed with the FEC, VoteVets spent almost $30,000 on TV ads targeting Burns in September. The New York City-based group ran similar ads against Republican senators in Virginia and Pennsylvania.

The goal of the VoteVets.org political action committee is to put Iraq and Afghanistan war veterans in Congress who are critical of the conduct of the war in Iraq, according to its website.

The U.S. Chamber of Commerce ran ads in Montana in support of Burns beginning mid-August and lasting about a month.

The pro-business group chose to advertise in the state because of Burns' record but also because his is one of the most highly targeted races in the country, said Renee Sinclair, director of congressional and public affairs for the group's Northwest region.

"Sen. Burns has been a good vote for business and he consistently ranks 88 percent or above on our scorecard of incumbent candidates," she said. "His views on natural resources are more in line with the state economy than we think Jon Tester's are."

The Chamber has said it plans to spend $20 million to help a variety of federal candidates this fall, partly with TV ads.

The National Rifle Association Political Victory Fund launched an advertising campaign last month in several Montana cities to help Burns, saying he has a strong history of supporting Second Amendment rights.

The NRA fund will run a total of 1,824 commercial spots on cable TV for four weeks, the group said. A report filed with the FEC showed that the NRA fund spent $19,200 on television ads supporting Burns, plus another $12,000 in production costs, in early October.