Maryland state Sen. Robert J. Garagiola officially launched his campaign for the redrawn 6th Congressional District on Tuesday, vowing to add a seat to the Democratic column and “break the petty partisan logjam in Washington.”

The seat is held by 10-term Rep. Roscoe G. Bartlett (R), who says he will seek reelection next year even though Democrats in Annapolis made the district ripe for a pickup by removing the more conservative eastern portions of the 6th and adding a slice of liberal-leaning western Montgomery County.

In the state’s new map, the redrawn congressional district includes Garagiola’s Montgomery-based senate district, though he promised at a Tuesday morning stop at a downtown Frederick bakery that he would work for everyone in the 6th, a key battleground as Democrats look to gain seats in the House.

“We are about a year away from taking this seat back, giving the voters a choice for the first time in 2o years . . . and we’re going to take this Congress back,” Garagiola said. “This is going to be ground zero.”

Garagiola has the support of some key local leaders, but he is not the only Democrat pursuing the seat. Former Montgomery County Council member Duchy Trachtenberg is running, and a handful of other Democrats — including former Montgomery County executive Douglas M. Duncan and investment banker John K. Delaney — are said to be considering bids. Neither Duncan nor Delaney returned calls seeking comment.

Garagiola’s congressional cam­paign follows his sharp tack to the left this year in the General Assembly, where he led efforts to legalize same-sex marriage and raise the state’s gas tax.

The positions are likely to boost his appeal with liberal voters in Montgomery County, who make up nearly half the reconfigured district’s voters, but the stances could undermine his appeal to the west, where the state is more socially conservative and rural residents vociferously oppose a gas-tax increase.

In interviews in recent weeks, Garagiola has downplayed concerns that his advocacy of same-sex marriage could hamper a congressional campaign, saying he is confident he could explain his position to potential constituents.

But he has stepped back repeatedly from the 10-cent-a-gallon gas-tax increase he advocated earlier this year and has not endorsed a blue-ribbon commission’s proposal for a 15-cent increase.

“At the federal level, I’m not advocating that we increase any taxes at this time,” Garagiola said Tuesday, adding that the General Assembly would “take a look” at the state gas tax when it reconvenes in January.

Asked how his same-sex marriage position would resonate in the congressional race, Garagiola said, “I just look at it as a civil rights issue, and I’m not going to run from it.”

Beyond those issues, Garagiola also has a nearly decade-long record of activism, recorded in thousands of votes taken in Annapolis. His extensive legislative record could appeal to Democratic voters but alienate independent and right-leaning ones.

Garagiola sought to make clear Tuesday that he was “an independent agent.”

“I’m a Democrat, but I’ve also been with [Gov. Martin O’Malley (D)] on some issues and not with him on others, and I plan to be that way . . . at the federal level,” he said.

Senate President Thomas V. Mike Miller Jr. (D-Calvert), who appointed Garagiola majority leader and who helped craft the new district, predicted the race will attract national attention because of its relative competitiveness and its proximity to Washington.

“People are going to come from West Virginia, Virginia, Pennsylvania, all around to campaign for this race. It’s going to be like the Civil War, like North and South coming together right there in Antietam,” Miller said, referring to the 1862 battlefield, which is in the district.

The 6th’s new lines have drawn criticism from Republicans and some Democrats for dividing up Montgomery County — and its growing number of minority voters — for the apparent purpose of adding another Democratic seat. But Garagiola portrayed the change as a positive one.

“Now it’s a district that a Democrat can win or a Republican can win. I think that’s good for democracy,” Garagiola said.

Maryland Republican Party Chairman Alex Mooney cautioned that the shape of the district may yet change. He said he remains confident that Republicans and a small grass-roots minority group, the Fannie Lou Hamer Political Action Committee, will raise the money needed to mount a legal challenge to the new boundaries.

As for the Republican field, it remains to be seen if the 85-year-old Bartlett has the desire to mount a multi-pronged attack to defend his seat. In the last fundraising quarter he raised just $1,000, leaving some state and national Republicans worried that he is not serious about seeking reelection.