As Democrats battle across Virginia to keep their narrow hold on the state Senate, the 31st District should be the least of their worries.

The seat is dominated by reliably liberal Arlington County. And although the newly drawn district now includes McLean, Great Falls and a slice of Loudoun County, the numbers still say Democrats should have a big advantage.

Yet as Arlington County Board member Barbara A. Favola (D) and businesswoman Caren Merrick (R) battle for the seat being vacated by retiring Sen. Mary Margaret Whipple (D), Republicans are gunning for an upset, and Democrats aren’t taking victory for granted.

“The district does lean Democrat, but it’s going to be a tight race,” said Del. Robert H. Brink (D-Arlington), who is backing Favola. “You have one candidate who has unlimited funding available to her and another candidate who has a record to run on. I think that’s the big difference.”

As she did during a hard-fought Democratic primary against lawyer Jaime Areizaga-Soto, Favola has emphasized her long service and familiarity with local issues. Favola said she had knocked on 30,000 doors and feels the campaign is “going very well.”

Merrick, the wealthy co-founder of an enterprise software company and a newcomer to politics, compares her current venture to her past ones.

“Campaigns are like a start-up,” Merrick said, “where you have a lot of goals and you’re building a team constantly and you’re executing a plan . . . and you have an exit.”

In this case, Merrick’s “exit” is Election Day, and she hopes it will lead to Richmond.

‘Side of the momentum’

After a run of strong elections for Democrats, Republicans reversed the tide statewide in 2009 and 2010 and are hoping to cap that run in next month’s legislative races by taking the Senate, which Democrats control 22-18.

Republicans think the wind is still at their backs, even in one of the bluest parts of the state.

“I think it certainly helps Caren Merrick, the environment where there still is more enthusiasm on the Republican side than the Democratic side,” said Mark Kelly, chairman of the Arlington County GOP. “You want to be on the side of the momentum.”

Kelly said Merrick was doing a good job appealing to independent voters by highlighting her efforts to start a business. “That’s experience she has and Barbara Favola doesn’t,” Kelly said.

In her own front-door pitch to voters, Merrick said, “I often tell them that I’m a technology entrepreneur and I’ve created hundreds of jobs.”

What she doesn’t typically say is that she’s a Republican. Merrick hopes that her profile — a political novice and businesswoman — will fit the current anti-establishment mood.

“That has been one of my goals . . . is to explain to them, ‘I am new to this, I bring a depth of experience and I am not a politician,’ ” Merrick said.

Voters across the country may be unhappy with incumbents, but Washington’s close-in suburbs are home to an atypically sophisticated electorate. So Favola and her backers are hoping that broad dissatisfaction with President Obama and Congress won’t trickle down into her race.

“I think people in the 31st District are knowledgeable and aren’t as swayed by the emotions of the moment as might be the case other places,” Brink said.

The fact that Republicans control the state House and the governor’s mansion will make some voters even more likely to back her and other Democrats for state Senate, Favola predicted.

“People really understand balanced government,” she said.

‘A good cross-section’

Under the old lines, the 31st District was relatively compact and strongly Democratic. Now it hugs the Potomac River, taking in more Republican-leaning territory. In his 2009 victory, Gov. Robert F. McDonnell (R) took 35 percent of the vote in the current district but drew 44 percent within the redrawn seat.

“I think that if you consider what’s here, it’s a good cross-section of Virginia,” Merrick said of the new district. “It’s urban, it’s suburban and it’s exurban.”

That variety means residents have different concerns, depending on where they live.

Favola said that Loudoun voters often mention education and transportation and that Great Falls residents cite the environment. But the largest chunk of the district — and Favola’s base — is Arlington.

“My Arlington voters are really values voters,” Favola said, and they give her marching orders: “You go down there and stand up for women’s choice and fight [Attorney General Ken] Cuccinelli’s agenda.”

That message is key to Favola’s strategy — defining Merrick as an ally of Cuccinelli and conservative groups that may not play well in this district. Favola has emphasized her support for abortion rights and reminds voters of Virginia’s new regulations for abortion clinics.

“She is listed on the Virginia Tea Party Alliance Web site,” Favola said of Merrick. “She definitely has ties to the tea party.”

Raking in campaign cash

Merrick’s wealth made her appealing to Republican Party leaders. But although she has put $51,000 of her own money in the race, she said she’s “not planning to” add any more.

“I don’t believe that’s the way to go, and I think that’s proven out in a lot of these federal races,” she said.

Neither candidate has had much trouble raking in cash.

Through Aug. 31, each woman had raised close to $300,000 for their campaigns — Merrick’s total includes the money from her own pocket — according to the Virginia Public Access Project.

As of that date, Merrick had $125,000 in the bank and Favola had $15,000, because the Democrat spent so much on her primary fight. But Favola said she had “raised a lot of money since then. I’ve had a very good month.”

Favola has gotten help from a host of big-name Virginia Democrats. She has events lined up this week with Whipple, Sen. James Webb, Rep. James P. Moran Jr. and once-and-future gubernatorial candidate Terry McAuliffe. She will be appearing with former governor Timothy M. Kaine this month.

Merrick has been aided by her own roster of state Republican allies, including McDonnell and his wife, Maureen; Lt. Gov. Bill Bolling; Susan Allen, wife of former senator George Allen; and Rep. Frank R. Wolf.

Although she has mostly touted her own background, Merrick has also sought to raise money by hitting Favola on her record.

In a recent e-mail to supporters, Merrick said she was facing an opponent “who has a record of attacking government workers with personal lawsuits to block transportation improvements, (costing taxpayers $2 million in legal fees), while raising taxes at every turn.”

Merrick’s reference is to the lawsuit filed by Arlington in 2009 — when Favola chaired the County Board — to block a plan to build high-speed toll and carpool lanes on interstates 95 and 395. Virginia officials dropped their plans to build HOT lanes inside the Capital Beltway this year, so Arlington dropped its suit.

Favola defends the lawsuit as the right move at the time, although she also thinks it will be irrelevant in this campaign.

“I don’t think it’s going to make a . . . difference,” she said. “Nobody brings it up.”