In much of the nation, campaign ads and election telephone calls are just another indication of the fall political season.

But these are rare events in North Dakota, where voters have not seen a tight Senate race in more than a quarter of a century.

The contest between Republican Rick Berg and Democrat Heidi Heitkamp is giving many people their first real taste of the untrammeled campaigning that has long been common in larger states, including a barrage of campaign advertising and calls.

The state's last competitive Senate race was in 1986, when Democratic Sen. Kent Conrad first won his seat. He is not seeking re-election.

On such voter getting the full experience of campaign politics this election cycle is farmer Mark Nesheim.

Nesheim was recently hustling to finish his wheat harvest when his cellphone rang. The caller wanted to know if he would support Republican candidates in November, particularly the North Dakota GOP's Senate hopeful.

"I don't tell anybody. I'm an independent," he said, explaining that the unwelcome questions put "three checks against" Berg.

When Conrad announced last year that he would not seek re-election, North Dakota assumed a leading role in the battle for control of the Senate. Republicans need to gain four seats. The GOP already dominates the North Dakota Capitol, holding most statewide offices and two-thirds majorities in the Legislature.

But Heitkamp, a former state attorney general and tax commissioner who is running her sixth statewide campaign, has been even with Berg, a freshman congressman who has run only one statewide race -- his defeat of incumbent Democratic Rep. Earl Pomeroy two years ago.

The wide-open race has attracted heaps of campaign cash. Political organizations such as American Crossroads, a group founded by Karl Rove, and Majority PAC, which supports Democratic Senate candidates, have spent more than $3.1 million on advertising in the North Dakota race.

That's close to $6 for every North Dakotan of voting age -- with the election still more than two months away.

"This is how elections work in most of the rest of the country," said Mark Jendrysik, chairman of the University of North Dakota's political science department.

"This is kind of the shape of things to come in American elections. Lots of untraceable money. Lots of spending. It's like an arms race."

The state's last competitive Senate race was in 1986, when Conrad first won his seat by 2,135 votes, beating incumbent Republican Sen. Mark Andrews.

Berg and Heitkamp are on pace to wage the most expensive Senate election in North Dakota history. The two candidates themselves raised $6 million and spent $3.2 million through June, according to disclosure forms. Berg alone spent $1.7 million.

Jendrysik expects the money mountain to grow even taller, possibly approaching $20 million.

Much of the money is being channeled into television spots. Political spending records from the KX Network, a group of CBS television stations in western North Dakota, show the intensity of advertising efforts by the campaigns and outside groups. The network ran 19 30-second advertisements focused on the Senate race on the evening of Aug. 28.

In most ads, Heitkamp is hammered as a stooge for President Barack Obama and Democratic Senate Majority Leader Harry Reid, who are portrayed as enemies of oil exploration and coal mining, which are significant industries in North Dakota.

Anti-Berg ads accuse him of wanting to cut spending on Medicare and farm subsidies, and claim that Berg has "gone Washington," a gibe the incumbent Republican congressman himself used against Pomeroy in 2010.

Delwin Petrick, who farms near Elgin, southwest of Bismarck, supports Heitkamp but is already weary of the ad warfare that aims to convince voters that each candidate is an agent of political ruin.

"They just turn me off, basically," Petrick said. "Most of the time when I see something that's lies on there, I'll vote for the other candidate."

He's not the only one questioning the air war. Some of the outside advertising has prompted a backlash, too.

In July, a U.S. Chamber of Commerce ad accusing Heitkamp of backtracking on her support of the new federal health care law was disavowed by Andy Peterson, president of the North Dakota Chamber of Commerce, who said the state organization was staying out of the Senate campaign.

"We're not participating in this or endorsing their action," Peterson told KFGO Radio in Fargo in July. "We made a conscious decision not to be involved."

Two years ago, North Dakotans got a preview of the advertising barrage when Berg thwarted Pomeroy's bid for a 10th term in Congress. Outside groups spent almost $3 million, while the candidates themselves spent $5.8 million.

Pomeroy believes spending by health insurers angered by his 2009 vote in favor of President Barack Obama's health care overhaul law helped seal his fate.

Berg and Heitkamp doubt whether the outside advertising is changing voters' minds.

"At the end of the day, it's a grassroots campaign that has the biggest impact on the outcome," Berg said.

Heitkamp said she didn't like any of the outside advertising, including ads supporting her own candidacy.

"I'm not convinced that this is all that effective, especially when it goes against what people think they know about the candidate," Heitkamp said. "People say, `Well, I know her, or I know him, and I don't believe any of that."'

Nesheim said neither candidate is waging the kind of race he wants to see.

"Their campaign, it stinks," he said. "They aren't telling the people ... what they can do in the Senate to help us. All they're doing is digging at each other. That absolutely goes against my better judgment in voting for anybody."