Del. Robert G. "Bob" Marshall (R-Prince William), the leading abortion foe in the state legislature, is being challenged by retired firefighter Bruce E. Roemmelt, a Democrat who has decided to fight Marshall with a different single issue: transportation.

Roemmelt said his strategy is to bypass Marshall's opposition to abortion, same-sex marriage and stem cell research by tapping into the public's increasing dissatisfaction with long commutes. Campaign contribution records show that Roemmelt has raised more money -- just over $107,000 compared with Marshall's $66,000 -- and Democrats and Republicans say he has assembled a broad grass-roots organization.

Still, leaders of both parties predict that Roemmelt's biggest challenge will be getting votes in the 13th District, which encompasses western Prince William County and part of Loudoun County -- areas Marshall has dominated since 1992.

The outcome of the Nov. 8 election may hinge on what voters consider most important: roads or social issues.

In the 2003 general election, Marshall, 61, ran unopposed. In 2001, he handily defeated lawyer Louis R. Brooks, who also used transportation as a campaign issue, capturing 65 percent of the vote.

"The numbers are not there for a Democrat to be elected at this time," said Brian Murphy, chairman of the Prince William County Republican Committee.

Rick Coplen, chairman of the Prince William Democratic Committee, acknowledges the conservatism of the district but is optimistic.

"Bruce Roemmelt is the right guy to pull off a come-from-behind win. There are pockets [of the district], clearly, that can be capitalized on by the Democrats," Coplen said.

Roemmelt's campaign staff has studied those pockets carefully, and Roemmelt said his door-knocking throughout the district has been highly strategic. In Virginia, voters do not register by party, but Roemmelt said he has identified voters who cast ballots in Republican and Democratic primaries and is targeting those who participate in Democratic contests.

Roemmelt, a native of Upstate New York whose first encounter with politics was as student government president at Lord Fairfax Community College in Middletown, Va., said he thinks he can topple Marshall with his message of "fix the roads, fix the roads, fix the roads."

"I have pledged to be the transportation delegate," said Roemmelt, 59. "We need a delegate who is going to focus on that all the time. . . . If I need my moral compass centered, I'll go to my minister."

Roemmelt favors stem cell research, describes himself as a moderate on abortion rights and says roads are not crowded "by gays getting married and going to the church for the ceremony."

Marshall, who grew up in Washington as the son of yellow-dog Democrats but switched parties when George McGovern ran against Richard Nixon for the presidency in 1972, said Roemmelt's campaign is misguided and is run by consultants.

Marshall said his social crusades in the legislature are prompted by the residents of his district. "It's important to a number of my constituents. This district is pro-life," he said.

Roemmelt's transportation plan includes a bus rapid transit system that he says would be cheaper than extending Virginia Railway Express, easier to complete and more flexible.

Marshall said the plan is shortsighted. "You have to have separate lanes for buses," he said. "You have to spend $530 million before you get to the Beltway. Then what the hell happens?"

The incumbent also defended his record on transportation, noting that he co-sponsored bills for the construction of the Route 234 bypass. "Does he have a private detective who walks around with me with a clock . . . to monitor my votes?" Marshall asked.

Roemmelt said Marshall has not done enough to complete road projects or to find ways to reduce traffic because he is too busy with his social issues. Simply placing more commuter lots closer to Interstate 66 could significantly reduce the number of vehicles on the road, Roemmelt said. "We need to reduce traffic to the point where families can eat together at home," he said.