Dulles Town Center, a 1.4 million-square-foot mall and cluster of condominiums just north of Dulles International Airport, is a new shopping mecca for the new suburban enclaves of Loudoun, America's fastest-growing county.

The sprawling mall keeps growing, with Hennes & Mauritz, the Swedish clothing retailer, arriving last year. Drivers entering from Route 28 pass wide tracts of open land where bulldozers churn the soil for the next subdivision.

The new landscape, far outside the Capital Beltway, could be pivotal in presidential politics this fall as Sen. John F. Kerry tries to win Virginia, a state that no Democratic nominee has won since Lyndon B. Johnson in 1964.

Loudoun and its neighbors along Interstates 66 and 95, brimming with new jobs and new arrivals, are home to some of the Massachusetts Democrat's most sought-after voters in the state's electoral powerhouse, Northern Virginia. And after Democrats largely passed by the area in 2000, the Kerry campaign is juicing up its investment this fall, with rallies, fieldwork and money.

President Bush defeated Al Gore in 2000 by just over 4,300 votes out of more than 800,000 cast in a region stretching from Arlington to Fredericksburg, statistics compiled by the University of Virginia Center for Politics show. But Kerry strategists say they believe the senator can pull out Virginia's 13 electoral votes this year.

In the Washington suburbs, the campaign is counting on demographic changes Kerry strategists say favor their candidate: an increase in voter registration in the immigrant communities of Alexandria, Arlington and Fairfax and a movement of Democrats to the ring of outer counties in search of less expensive housing than they can afford closer in.

"We're seeing families moving out because of affordability issues," said Jonathan Beeton, Kerry's spokesman in Virginia. "They are more middle class and lower middle class people, who tend to vote Democratic."

But strategy meets reality in Loudoun, a county that gave Bush 56 percent of its votes in 2000. Most shoppers at the town center one afternoon last week said their conservative values and support for the war in Iraq will put them solidly behind the president in November.

"The president's faith is obvious, and I just think Kerry's been inconsistent with his views," said Loretta Ford, 51, who with her husband runs a drilling company that is thriving in the hot home-building market. Ford, who lives in Sterling, said she is staunchly against abortion and embryonic stem cell research.

Stefan Mandanis, 38, who moved to Ashburn from Maryland in 2002 and was on a day off from his job at a systems integration firm, also cited the president's concern for "what matters for me and my family morally" and believes Bush returned a "civility" to the White House that was lost during the Clinton years. Although Kerry supporters point to Bush's falling popularity abroad because of the war, Mandanis, who supported the Iraq offensive, called the criticism misplaced. "This war is not about being the best friend of every country in the world," he said.

As a voting bloc, though, the Washington suburbs are far from monolithic, encompassing new-economy workers like Mandanis and the Fords, Korean and Latino shopkeepers, technology titans, federal government employees. They tend to split between Democrats inside the Beltway and Republicans outside. By and large, they are educated and consider themselves well-informed. And while Kerry and the president spar over the nation's slow job growth, the Northern Virginia economy keeps humming.

Closer to Washington, in Fairfax County, mixed views of the candidates were expressed by a sample of commuters in the county's closest district in the 2000 presidential race -- Braddock, which went to Bush by 1,115 votes. At the Burke Centre Virginia Railway Express station last week, voters were split evenly between Bush and Kerry, with several pledging to vote Democratic this year after supporting the president in 2000.

"I've been disappointed in Bush's performance in Iraq," said John Boyle, 45, a consultant for NASA, as he waited for his wife's commuter train, his toddler in tow. "The terrorists have been emboldened. There was no concern about the aftermath. And I think I've been lied to about why we went in." Boyle voted for Bush four years ago, "mainly because of Clinton fatigue." Now, "it's kind of sad that I'm not comfortable voting Republican."

Bush strategists scoff at the idea that Kerry could win in Northern Virginia, saying the Democrats have no evidence that new arrivals to Prince William, Loudoun, Stafford and western Fairfax counties are less conservative than the Republican voters who supported Bush in 2000. And they say the region's strong economy will help the president.

"You have to look at Northern Virginia not geographically but economically," said Kevin Madden, the Bush campaign's northeast press secretary. "It's a burgeoning small-business economy. Small businesses would be devastated by Kerry's fiscal policies of rolling back the president's tax cuts."

But the Kerry campaign is pushing hard nonetheless, drawing close to 800 supporters to the opening of its Merrifield headquarters last month, Beeton said. The Northern Virginia operation has five full-time field staff members. Female Democratic leaders recently held a rally for women in Arlington. And Elizabeth Edwards, the wife of Kerry's running mate, Sen. John Edwards (N.C.), has scheduled a visit to Alexandria this week, the campaign said.

Kerry supporters are focusing attention on Hispanic voters, whom they see as a key to a victory in Northern Virginia. The campaign's most visible surrogate is Democrat Walter Tejada, an immigrant from El Salvador elected to the Arlington County Board last year.

"Are we better off than we were four years ago?" Tejada asked a group of Hispanic business leaders and Kerry supporters gathered for lunch in Arlington last week. "The answer is no. There was hope for the Latin community because [the president] spoke some Spanish. . . . But it's gone now."

Voter registration has jumped in the Washington suburbs, although Virginia does not register voters by party, so it is impossible to determine the newcomers' preferences. Prince William counted 184,150 registered voters as of last week, up from 156,435 in 2000, election statistics show, while Loudoun counted 135,592, up from 104,394 four years ago. Registration in Alexandria and Arlington, meanwhile, was largely stagnant.

Prince William Democrats, outnumbered on the county board and in the General Assembly, nonetheless say they are seeing a surge of grass-roots work for Kerry as the election nears, at house meetings and gatherings of the local committee. Board of County Supervisors Chairman Sean T. Connaughton, a Republican, said he believes most newcomers to the fast-growing county are independent or Republican-leaning voters.

"They tend to be more conservative on security issues and on what they expect from government," he said. But he acknowledged that Bush cannot win Prince William by counting on party activists. "We have to work hard for votes," Connaughton said.

But it is Fairfax, the county sandwiched between Arlington and Alexandria to the north and east and Loudoun and Prince William to the west and south, that will be the powerhouse in Northern Virginia on Nov. 2. No Democrat has won statewide office without winning Virginia's most populous county, which accounts for almost two-thirds of the region's registered voters. The county swings left and right, narrowly favoring Bush (with 48 percent of the vote) over Gore (with 47 percent), Gov. Mark R. Warner (D) over Mark L. Earley (R) in 2001 and County Board of Supervisors Chairman Gerald E. Connolly (D) over Republican Mychele B. Brickner last year.

"Certainly Fairfax County is in play, much more dramatically than four years ago," said Connolly, who plans to speak as a Kerry surrogate. "Democrats are energized. This is a moderate county, a swing county."

Yvonne Watson, 37, a federal worker, is just the kind of voter Connolly is talking about. Stepping off the commuter train at Burke Centre in central Fairfax, she said she is undecided and "needs to do research" on the candidates' platforms. As with the president, she said, her faith guides many of her decisions. But, she added, that does not necessarily mean she will vote for him.

Yvonne Watson of Burke said she is undecided and "needs to do research" on the candidates' platforms. Other commuters at the Burke Centre VRE station in Fairfax County were split evenly between Bush and Kerry.Matt Herbert, 48, of Burke was one of several people at the Burke Centre VRE station who said they plan to vote for John F. Kerry after supporting President Bush in 2000. Herbert said a brother who lost his job in Michigan and America's tainted image abroad have influenced his choice.