Is GOP Sen. Scott Brown an independent, common-sense voice for Massachusetts, or is he poised to be the 51st vote in support of a Senate with a tea party agenda?

Competing memorandums from the Massachusetts Democratic Party and Brown’s campaign are set to hit inboxes later today, both hoping to frame the narrative of an important, competitive Senate race 13 months before the election.

“The choice for Massachusetts is stark,” state Democratic Party Communications Director Kevin Franck wrote. “Elect a senator who will be a voice for the middle-class or send [Minority Leader] Mitch McConnell [R-Ky.] the 51st vote he needs to give Tea Party Republicans control of the U.S. Senate.”

That’s hardly the storyline Brown campaign manager Jim Barnett emphasized. Brown is “viewed as an honest broker who connects with people because he’s an open-minded and independent thinker who does what’s best for Massachusetts,” Barnett wrote.

Barnett also wrote that his candidate was focused on jobs and “has made it his mission to reduce taxes, spending, over-regulation and the size of government ­— all of which are making economic recovery more difficult.”

But state Democrats are trying to undermine Brown’s case that he is an independent voice.

“While Scott Brown is likely to highlight the few times he has broken from Tea Party Republican orthodoxy to vote with Democrats, it’s worth pointing out that those measures would hardly have had a chance to advance in a Republican Senate,” Franck wrote. He cited Brown’s vote to overturn the military’s “don’t ask, don’t tell” policy, which he posits would never have reached the Senate floor if McConnell were in charge. He also framed Brown’s vote in favor of the Dodd-Frank financial reform act as something the Bay State’s junior Senator only voted on “after making sure that the banking industry would not be on the hook for the cost of implementing new reforms.”

While telegraphing the broader points of the strategies that both sides will deploy over the next year, the memos also tapped into tried-and-true party talking points.

“A Tea Party-controlled Senate would double-down on the failed economic policies of the past, continuing tax breaks for Big Oil companies, CEOs and hedge fund managers while insisting that the full burden of getting our nation’s fiscal house in order be placed squarely on the shoulders of the middle class,” Franck wrote, echoing the standard Democratic line.

“Whomever Democrats nominate for U.S. Senate next September will invariably support the same failed tax, borrow and spend policies that keep our economy teetering on the brink of recession, [and] millions of Americans in the unemployment line,” Barnett wrote, echoing standard Republican fare.

Neither of those party lines will necessarily be the most effective with the Massachusetts electorate. The Bay State is strongly Democratic — Democrats control the Legislature, the governor’s office and every seat in the U.S. House — but the majority of voters are registered with no party and have, in certain circumstances, shown a willingness to vote for the GOP. Republicans ruled the Bay State governor’s office from the end of Democrat Michael Dukakis’ term in 1991 until Gov. Deval Patrick was sworn into office in 2007.

The independence of the Massachusetts voter is a theme Barnett tapped into in his memo, which was sent to Roll Call after inquiries about the Democratic memo released to Roll Call on Sunday.

“A large proportion of Democratic general election voters will be more moderate and conservative ethnic and working-class voters who appreciate Scott Brown’s common-man appeal and common-sense policies,” Barnett wrote. “They helped deliver victory to Scott in 2010 and will be a key group within Scott Brown’s winning coalition in 2012.”

Franck, of course, hammered home a different take in his memo, writing that the Bay State “is overwhelmingly opposed to the national Republican agenda.” He cited one recent poll showing that voters favor broad strokes of the Democratic agenda, including narrowing the gap between the richest and the poorest Americans and raising taxes on the wealthy.

Without giving away third-quarter fundraising numbers, Barnett wrote that Brown’s “[f]undraising over the last year has been especially solid.” At the end of June, Brown had almost $10 million in his campaign account, according to Federal Election Commission records.

Harvard professor Elizabeth Warren, the frontrunner in the race for the Democratic nomination, has only been in the race since mid-September. She appears, however, poised to post substantial numbers for the few weeks she has been an official candidate in the race.

Recent polls have shown Warren, who has strong support from both a national liberal base and the establishment Democrats in Boston and Washington, not far behind Brown in a head-to-head matchup.

Roll Call rates the Massachusetts Senate race a Tossup.

Narratives sometimes define campaigns as much as the candidates themselves, so it’s no surprise that both sides are trying to frame the election in vastly different ways 13 months out.

But there’s one thing both Barnett and Franck can agree on: There’s a lot at stake in the Massachusetts Senate race in 2012.