Donald W. Patterson Jr., a Northern Virginia Democrat, picked up a whiskey bottle, set it on the stage floor in front of him and launched into a talk about what he saw as Virginia's need to get tough with drunk drivers.

Though the bourbon bottle was empty, it added an unusual touch of flamboyance to Patterson's uphill campaign to unseat Republican Del. Kenneth B. Rollins in the Nov. 2 special election. Rollins, a former Leesburg mayor and Loudoun County judge, is considered the front-runner in a newly reshaped House of Delegates district that includes most of Loudoun and part of neighboring Fauquier County.

Drunken driving has become an increasingly volatile issue in Northern Virginia. A 25-year-old Fauquier man was convicted of drunken driving and second-degree murder last month in the deaths of three Fauquier residents in a head-on collision. A Loudoun teen-ager was among six Northern Virginia residents killed in a crash on a rural highway west of Winchester, Va., in which a West Virginia man was found guilty earlier this year of drunken driving and involuntary manslaughter.

Patterson, a millionaire Fauquier businessman, seized on the issue at a political debate a few nights ago, calling for stiffer drunken driving penalties and accusing his Republican opponent of showing "sympathy for drunk drivers." Rollins sharply rejected the charge, asserting that he had supported a stringent new drunken driving measure at this year's General Assembly session.

"We passed one of the toughest laws in the country," Rollins contended later, criticizing Patterson as "misinformed."

Many Northern Virginia Democrats view Patterson's choice of issues, including drunken driving, as one sign of skillful campaigning against considerable political odds. A recent poll by The Loudoun Times-Mirror gave Rollins 41 percent to Patterson's 21 percent, with 38 percent undecided. A later poll by Loudoun radio station WAGE showed Rollins ahead by a narrower margin of 38 percent to Patterson's 31 percent, with 31 percent undecided.

Rollins, 46, is regarded as the front-runner partly because he is a well-known political figure in Loudoun, which accounts for more than two-thirds of the district's registered voters. Republicans, moreover, have shown marked gains in Northern Virginia. Last year, Rollins himself unseated a Democratic incumbent, Earl E. Bell, by a sizable margin, 7,996 to 6,913.

Patterson, 44, who has run for political office only once before, was defeated in 1979 for the state Senate by Minority Leader William A. Truban in a five-county district centered in the Shenandoah Valley. Patterson carried Fauquier but lost in the other counties. Nonetheless, many politicians, including Truban, conceded that Patterson ran an energetic door-to-door race while spending lavishly on his campaign.

Patterson, who is renovating an office building in the Fauquier town of The Plains and also heads an energy consulting firm, is married to the former Andrea Currier, a member of the Mellon family.

"Mr. Patterson is well-financed. He's a multimillionaire," Rollins asserted in an interview. "And he's spending it." Patterson acknowledged that he probably would outspend Rollins and said he is prepared to finance a portion of his campaign costs from his own pocket. He declined to discuss his personal wealth.

Rollins has stressed his more than 20 years in public office, describing himself as "the only member" of Virginia's General Assembly to have served in all three branches of government. He was elected to the House of Delegates as an independent in the early 1970s, but was defeated by Bell and two other Democrats in a three-member district in 1975. When Rollins recaptured the seat from Bell last year, the contest took place in a redrawn, single-member Loudoun district.

This year's special election in the new single-member, Loudoun-Fauquier district resulted from court-ordered redistricting.

Another issue in the Patterson-Rollins race is development, a controversial topic in the largely rural counties. Patterson has sought to portray Rollins as an advocate of excessive growth and has said he disagrees with Rollins about a proposal that would give the Loudoun Board of Supervisors broader authority to regulate development. Rollins has expressed reservations about the board's proposal; Patterson says he supports it.

Replied Rollins: "I think the county has ample tools on that now."

Highways, an issue that Rollins employed in his 1981 race against Bell, remain a point of contention. Many residents complain of poorly built, unsafe roads and insufficient state spending for rural highways. "What we need to do is change the highway financing law," Rollins argued. "We came within one vote of winning that."

Patterson counters by accusing Rollins of showing inadequate leadership on this issue. "What has been done since he's been representing this district?" Patterson asked. "Nothing."