When Robert M. (Bob) Gants decided to run for the 45th District seat in the Virginia House of Delegates, he knew his race would lead in only one direction: uphill.

Gants is a first-time candidate; his opponent, Democrat Marian Van Landingham, is a six-year incumbent. Gants is a Republican; the district, the eastern half of Alexandria, is one of the most Democratic in the state. Gants is a relative unknown; Van Landingham, while not a household name, is a longtime fixture on the city's civic league circuit.

But Gants, a 50-year-old lobbyist and former Capitol Hill staff member, is betting that what sells in Washington will also sell in Alexandria and Richmond.

"I know how to get things done in Congress and a legislature," Gants said recently. "I look at it as practicing preventive law instead of remedial law. I have been successful in getting good laws passed and bad laws killed."

Van Landingham, 50, a self-employed public relations specialist, says Congress and the General Assembly are separated by more than just a 100-mile drive. "Richmond doesn't work like Washington, and I don't think Mr. Gants realizes that," Van Landingham said.

"There's no way to get the experience you need to understand Richmond except to go there. I've done that already, and Mr. Gants hasn't. I don't think Mr. Gants has given the voters any reason not to send me back."

The district that Van Landingham and Gants hope to represent after the Nov. 3 election takes its politics seriously. The 45th District is dominated by Old Town, an affluent neighborhood of Federal Period row houses and trendy shops. Old Town residents are highly organized and traditionally have controlled city politics. They have opinions on everything from local rezonings to nuclear weapons.

Generally, those opinions are liberal. In 1984, when President Reagan's conservative Republican landslide swept 49 states, he got 44 percent of the 45th District's vote. In 1985, GOP gubernatorial candidate Wyatt B. Durrette picked up only a third of the district's ballots.

One of the few Republicans to do well in the 45th is state Sen. Wiley F. Mitchell, a relatively liberal legislator who was Alexandria's vice mayor before going to Richmond. But even Mitchell, who is running unopposed this year in the 30th Senate district, does not win easily here; in 1983, he pulled in 53 percent of the vote.

Gants and Van Landingham agree that the campaign's major issue is the area's rapidly increasing traffic problem. Van Landingham voted last year for legislation that raised taxes to build roads, but Gants says the state does not spend its money efficiently, and he says he would have opposed the tax increase.

"Ms. Van Landingham has voted for every tax increase to come down the pike," Gants said. "How about fiscal responsibility? We don't need new taxes, we just need to cut the pie differently so Northern Virginia gets its fair share of the state's money."

Van Landingham said the legislation gave Northern Virginia millions of dollars in new money for road construction and Metrorail subsidies. "I haven't heard any complaints about the additional taxes," she said.

Van Landingham is no stranger to her constituents. She was active in the founding of the Torpedo Factory, a showcase for the arts on Alexandria's waterfront, and she maintains a painting studio there. She won the Alexandria Chamber of Commerce outstanding service medal in 1976 and was named Washingtonian magazine's Washingtonian of the Year in 1974.

"We have an intelligent, fairly sophisticated electorate in this city . . . . These people have been involved in their community," Van Landingham said.

"Mr. Gants has lived here for 18 years, but he never bothered to join the Old Town Civic Association. I don't think he has a community base."

Gants, who says he founded a civic association in his neighborhood, says he offers different experience. A graduate of West Point and American University Law School, Gants went to work as a staff member in the House of Representatives about 15 years ago. He was administrative assistant to former representative John Anderson, a 1980 presidential candidate, and he worked in the executive branch bureaucracy during the Nixon administration.

He began work as a lobbyist in 1980 and now is executive director of the Home Appliance Manufacturers Association. During his tenure with that group, Gants says, he built a coalition that helped pass legislation setting energy efficiency standards for appliances such as refrigerators and air conditioners.

"I'll stand on my record anytime," Gants said. Van Landingham's civic involvement "gives her a base, but it doesn't make her a good legislator," he added. "I've been active in community affairs, but I also know how to get the job done in government."

Van Landingham says she hopes to raise about $40,000 for her campaign; Gants is shooting for around $25,000. Gants has run ads on the city's cable television system, but Van Landingham said she will run a traditional campaign with little mass media advertising.