In a race that could decide control of the Senate this fall, the two very different contenders for the seat once held by the late Sen. Edward Kennedy are selling themselves with essentially the same story.

Sen. Scott Brown (R) and Harvard professor Elizabeth Warren (D) both want to be seen as regular, plainspoken folks — outsiders who will make their voice heard battling against entrenched interests. And each wants his or her opponent to be seen as part of those entrenched interests.

“They’re both trying to climb the same side of the hill,” said one influential Bay State Republican, discussing the candidates’ messaging. “And the independents are the ones they’re both going after.”

The election is still eight months away. And while Brown has led in a series of recent polls, top strategists of both parties expect the race to be a margin-of-error contest by November. That’s part of the reason the narrative will be so important and why, when their narratives are distilled, both candidates are telling the same story to swing voters.

It’s a story that has worked for years: It helped Kennedy, the Democratic scion, hold the seat in his race against Mitt Romney (R) in 1994.

“I think that’s what we want in a Senator,” said Democratic consultant Scott Ferson, who served as Kennedy’s press secretary from 1990 to 1995. “I always go back to the slogan of his campaign in 1994: ‘His voice is always heard.’ We want our Senators to stand out” from the establishment.

It’s a story that appeals to a particular swath of independents — blue-collar, working-class and often in a union — in a state where a majority of registered voters aren’t enrolled in either party.

Warren kicked off her campaign at a subway stop in South Boston and recently appeared in that blue-collar section of the city with members of the local pipefitters union. “My campaign is all about working people,” she told the Boston Globe in February.

Brown, too, has been relentless in putting forth the image that he understands that group of voters so well because they’re embedded in his own life story.

“Working-class people are a natural constituency for Scott Brown because he is one of them,” Jim Barnett, his campaign manager, told Roll Call. “He speaks their language, he relates to their lifestyle, and he shares their values. He’s a regular guy and that’s an important part of his appeal.”

Indeed, Brown wants to be seen as a regular guy who is reaching across the aisle, diligently working to get things done — and has. He sees himself as the underdog, the position he’s been in his whole life. His story: He has been fighting, against the political odds, to take on the deeply rooted political machines in Boston and Washington, D.C., for the sake of Bay Staters.

Warren wants to be seen as a normal, everyday person — a gutsy fighter for the middle class, who grew up on its “ragged edge.” Her story: She’s been fighting for the little guy against the big banks and their allies her whole career. And the big Wall Street fat cats and their compatriots will do anything to keep her from getting to the Senate.

Of course, the campaigns and their surrogates will blast their own narratives about their opponent.

Warren is “not credible when she says ‘I’m one of you,'” said Brad Card, a Republican lobbyist in Washington, D.C., who is a Bay State native and familiar with the Brown campaign.

“The ironworker from South Boston is going to look at Scott Brown — see his jacket, his truck, hear that he sounds like them, that he grew up playing basketball, goes to Sox games and Patriots games. And then you have this woman who is from Oklahoma, is a professor at Harvard and lives in a multimillion-dollar home in Cambridge,” he explained, echoing Brown’s line that Warren is an “elitist.”

Democrats who understand the voters both candidates are courting vociferously defend Warren’s middle-class cred.

“People want to try and take a shot at her because she happens to be smart enough and qualified enough to be a professor at Harvard,” Boston City Councilor Mike Ross (D) said. “But she knows of what she speaks: That middle-class world is the world she grew up in.”

Democrats in the state said that while those key working-class voters are in play, they voted for a promise in the 2010 special election Brown won but haven’t seen results that will sway them to vote Republican again this year.

“I’ve seen plenty of elections in Massachusetts where union guys vote Republican,” longtime Bay State Democratic strategist Mary Anne Marsh said. But she said Brown’s appeal has probably run its course with a lot of those conservative-leaning blue-collar workers. “The barn jacket in South Boston got him the first round, but that’s not putting food on the table for them now — and they’ve been out of work a long time and he’s done nothing for them down in Washington.”

Watch for Democrats to tie Brown to D.C. Republicans. On at least one issue, Warren has described Brown as being “with Washington and Republican extremists and against the people of Massachusetts.”

That’s an accusation Brown partisans see as laughable given his record of voting with both Republicans and Democrats.

Democrats scoff at the idea he’s an underdog who is fighting against the establishment. They see Brown, an incumbent Senator with $13 million in the bank and two decades in elected office, as part of the establishment.

While Warren has her work as a consumer advocate to point to as a bolster to her pitch to voters, Brown has the double-edged sword of a Senate voting record. He’ll use his 2010 Congressional Quarterly ranking — he voted with his party only 54 percent of the time in votes where a majority of Democrats opposed a majority of Republicans — to bolster his claim of independence.

Democrats will hammer him on his votes such as one for the controversial contraceptive care amendment authored by Sen. Roy Blunt (R-Mo.).

In the end, Republicans believe Brown’s story will ring more true to voters because he has his Senate record to back it up.

“Scott’s narrative speaks for itself because he’s had the opportunity to prove it,” the influential Bay State Republican said. “She’s saying ‘trust me.'”