Not since L. Douglas Wilder's historic run for governor in 1989 has a Democrat captured a majority of the vote for governor in Loudoun County. Democrats in Prince William County have been waiting even longer.

But Virginia Gov.-elect Timothy M. Kaine (D) won both in Tuesday's election. Republicans needed to win big in the outer suburbs to offset heavy support for Kaine in areas closer to Washington, and their failure to do so was one of the keys to the defeat of Republican Jerry W. Kilgore.

Kilgore slipped in areas where Republicans have been so dominant that they control the local boards of supervisors, sheriff's offices, commonwealth's attorney posts and most delegate seats.

Kaine reached out to voters in these rapidly growing outer communities who are accustomed to the dust and traffic that come with new homes. The Democratic candidate proposed new tools for local governments to slow growth if they found that traffic would overwhelm the roads.

"Kaine ran this commercial on a big ad buy that showed bulldozers and said: 'I hear you. I'm on your side with this,' " said Robert E. Lang, director of the Metropolitan Institute at Virginia Tech. "He said what needed to be said, and he showed those bulldozers -- and people got that."

Loudoun Board of Supervisors Chairman Scott K. York (I), who parted ways with the local Republican Party after advocating slowing growth, called the maneuver a "brave" introduction of a hard issue of concern only to local voters.

"These are issues that are concerning folks, and it's not about Republicans or Democrats," he said.

Kaine won Loudoun by almost 6 percentage points and Prince William by 2. He bettered Democratic Gov. Mark R. Warner's tallies from 2001 in the two counties by more than 16,000 votes, while Kilgore added only 4,768 votes over 2001 Republican candidate Mark L. Earley.

More than 23,000 additional votes were cast in the two counties this year compared with the 2001 statewide elections, a function of the home construction that has brought thousands of new voters to the region and made Loudoun one of the fastest growing counties in the country, with Prince William not far behind.

Loudoun County's Precinct 813, with more than 5,800 registered voters, backed President Bush over Sen. John F. Kerry (D-Mass.) by 53 to 46 percent, but its voters picked Kaine over Kilgore by 55 to 43 percent.

As voters emerged from their polling place at an elementary school, they were met by representatives of Campaign for Loudoun's Future, a group advocating restrictions on development. They stood next to a map of the county showing areas approved for new subdivisions and handing out stickers saying "Don't Supersize Loudoun."

"To me, the growth issue and the roads issue are almost one and the same," said David Smith, 46, a resident of the precinct who voted for Kaine in part because of the issue. "They didn't plan for the growth here. The roads should have [been] built a long time ago. [If they keep building] you'll have a quagmire here, and it's really going to hurt the quality of life."

This precinct had not been drawn when Warner was elected governor -- and not a single home had been built in the massive Lansdowne on the Potomac development surrounding the school where Smith voted.

Studies show that a larger proportion of new residents moving to the outer suburbs in the past few years are immigrants, creating a diversifying population whose voting patterns may have also aided Kaine.

"There has to be a reason for this, and for me the reason is the influx of the new people, and the biggest chunk of that influx are foreign-born citizens," said Mukit Hossain, president of the Virginian Muslim Political Action Committee.

Hossain said his group, which endorsed Kaine, compiled a comprehensive database of Muslim voters in Virginia, finding that about 15,000 of 49,000 statewide live in Prince William and Loudoun. Many legal immigrants in the area were turned off by Kilgore's pledges to use state police to fight illegal immigration and his opposition to a proposed taxpayer-funded day labor site in Herndon, and voted accordingly, he said.

The group also endorsed Democratic delegate candidate David E. Poisson, who unseated Richard H. Black (R-Loudoun), one of the most conservative House members. Hossain said an analysis of survey data showed that more than 60 percent of Muslims in Poisson's district voted and that they supported the Democrat by more than 30 to 1.

"If the politicians have any sense, I'd hope they'd pay attention," said Hossain, who also works with the group trying to start the Herndon center.

Newcomers to the counties, who move from all over the country, also tend to characterize themselves as independents rather than partisan voters, Lang said, putting the outer suburbs in play like never before.

"How many of them are from places like Long Island, Connecticut, suburban New Jersey, Pennsylvania? Lots. And they come not with liberal politics. What they come with is suburban moderate politics," he said.

Gary Holt, 48, who moved to Loudoun from Florida a little over a year ago and voted for Bush in the 2004 election, voted for Kaine over Kilgore because "I didn't like how the Republican ran his campaign. He didn't focus on the issues important to me -- he just focused on the negative."

Black predicted that the Democratic success would be temporary and was more the result of Bush's unpopularity than any fundamental changes within the county.

"I think this is an anomaly, and my guess is it will not last for long," he said.

He argued that division within Republican ranks hurt their own efforts, diluting the party's brand name when members voted with Democrats and Warner in 2004 for a plan that provided new funding for state services through higher taxes.

"When we try too hard to look like Democrats, people say, 'What's the difference? Why not just vote for Democrats?' " he said.

Other Republicans drew exactly the opposite lessons, arguing that their party needs to spend time analyzing how to solve transportation problems in Northern Virginia, particularly as the boundaries that have traditionally separated the region's more rural and suburban areas erode.

"We are almost seamless now in this region. Culturally, we're becoming separate and almost insular from the rest of the state," said Sean T. Connaughton (R), chairman of the Prince William County Board of County Supervisors.

"Northern Virginia is going to continue to grow at a tremendous rate and become wealthier. We Republicans cannot win in a statewide election if these trends continue," Connaughton said.

Gov.-elect Timothy M. Kaine (D) defeated Jerry W. Kilgore in a Loudoun precinct where President Bush won in 2004.