Washington area residents share a reverence for the same snaking river, get snarled in the same inching traffic, sweat in the same soggy air and enjoy the same upsides, annoyances and dangers that come with the seat of American power.

It's a region that takes pride in how it cooperates across county and city lines on such crucial issues as homeland security, law enforcement and transportation.

But a dust-up over the right place to host a Major League Baseball team -- the nation's capital city or the country's fastest-growing county, 20 miles west -- is pitting area residents and officials against one another in a way that reopens old city vs. suburb debates.

At play are not only different financing packages, surroundings and business models but also, for some, conflicting worldviews. In the District, many people openly mock the idea of a stadium near Dulles International Airport, which they view as the outer end of one of the most congested traffic corridors in the region. And in Loudoun County, where officials are careful not to directly deride the District, they nonetheless tout the wealth and population of the suburbs.

The local and international competition to be the new home of the Montreal Expos leaves Major League Baseball as the ultimate winner, experts say.

"Baseball's got the upper hand as long as the cities . . . are going to try to outdo each other," said Rick Eckstein, co-author of "Public Dollars, Private Stadiums: The Battle Over Building Sports Stadiums." "They just love it. It's good for them as a business."

Both of the Washington area proposals have their drawbacks and uncertainties. But with baseball officials promising to decide where to move the Expos sometime after Tuesday's All-Star Game, advocates from the District tout its urban setting while Loudoun supporters boast of the growth and advantages of the suburbs.

"It's inconceivable to me that anybody from Washington, D.C., would schlep all the way out there to go to a ballgame," said Tony Bullock, communications director for D.C. Mayor Anthony A. Williams (D). "It's a hellish commute any time of day, but especially between 4 and 7 o'clock in the afternoon."

For the 2 million Northern Virginians, the region is just as worthy, the bustling population center of a state with an important patriotic history and long-held major league aspirations.

William L. Collins III, head of the Dulles investment group, breezily cites his side's advantages. "If you're a business looking to relocate any place in the country, your choice would be Northern Virginia," he said. The shopping, good schools and good jobs "make this the best place to live and raise a family in America," he said.

Which bid could win over baseball's Relocation Committee really depends on a jumble of concrete and intangible factors, say people who have studied baseball's previous dances with cities pining for expansion teams. Eager would-be hosts in Virginia and the District have moved into that sometimes-uncertain territory with packages filled with enticements, concessions, promises and a generous allotment of hype, all meant to stir cagey Major League Baseball executives.

Tom Chema, a leader in the development and construction of Jacobs Field, home of the Cleveland Indians, said major league officials are looking for a community that will make money for baseball owners for the long haul.

"What they want is a market that is going to be contributing to the shared revenue pot, not take away from the shared revenue pot," said Chema, chairman of Gateway Consultants Group. "After the blossom is off the rose a little bit, does your . . . team still have the economic staying power?"

Answering that question has been a key task for the backers of the region's rival bids.

What's on the table in the District is a proposal to build a 41,000-seat ballpark in the heart of the nation's capital. The city has identified four potential sites, one of them a short walk from the Mall. All four are near Metro stops, and two already have access to ample parking. The trend in the majors is downtown ballparks near public transit.

Williams and other city officials have vowed to fully fund construction of the stadium, which is projected to cost $278 million to $383 million, depending on the site. The team would pay nothing if it chooses the cheapest location, on the grounds of Robert F. Kennedy Memorial Stadium. At the other sites, the District is proposing to charge the team as much as $5 million a year in rent.

The proposal also includes $15 million to quickly renovate RFK so the team would have a place to play while the new ballpark is built.

But some on the D.C. Council question the financing plan. Council members Adrian M. Fenty (D-Ward 4) and David A. Catania (R-At Large) write in a letter in today's Outlook section, "Bringing a major league baseball team back to Washington would be great for the District, but not if the price is a huge public subsidy."

Gabe Paul Jr., the Virginia Baseball Stadium Authority's executive director, wrote two months ago to Major League Baseball officials that they should "separate fact from fiction and myth from reality" in examining the competing proposals. "While other jurisdictions may have plans to enact financing legislation, Virginia has had all the legislation we need in place since 1997."

Washington's history with sports franchises raises other questions about attendance. Professional sports teams struggle to fill the seats at their downtown Washington homes.

Supporters of the D.C. bid have suggested that the attendance projections for a Virginia stadium might be too rosy. But backers of the Dulles stadium counter that Loudoun is an obvious place for a major ballpark development. A 450-acre community would rise in a boom town.

Developers would build 5,400 condominiums or apartments, more than 850 single-family homes and 5 million square feet of commercial space around the ballpark. They would supply land for the stadium, build a massive parking lot, add interchanges and stretch sewer lines, covering $82 million of the costs associated with the 42,500-seat stadium, according to the financing plan presented to Major League Baseball.

Team owners would pay nothing up front but would cover one-third of the $360 million stadium total in rent payments. The Stadium Authority, responsible for building the stadium, would cover the other two-thirds, using taxes on ballpark-related spending, such as on concessions and players' salaries.

The stadium would be financed with $418 million in public bonds backed by the "moral obligation" of the commonwealth, meaning Virginia pledges but is not legally bound to repay any shortfall, according to authority spokesman Brian Hannigan.

The Loudoun project would need approvals from the county board, but it has strong support there.

Some D.C. officials question Northern Virginia's assumption that its ballclub could use RFK Stadium as a temporary home. RFK is controlled by the D.C. Sports and Entertainment Commission. Its chairman, Mark H. Tuohey III, said in an interview that the commission would consider such a request if it crossed his desk. But unlike a hometown team, Tuohey said, a Northern Virginia ballclub would not be given automatic rights to the stadium.

Hannigan said that officials in Virginia have been assured that D.C. officials would have no problem granting access to RFK and that Rep. Thomas M. Davis III (R), a House leader from Northern Virginia who has oversight of the District's operations, would lend his support to the effort.

Financing for a transit link to the Dulles site is another uncertainty. State and local officials in Virginia hope to extend Metrorail 23 miles to the Dulles area, at a cost of about $4 billion, with substantial funding from the federal government. But so far, the Federal Transit Administration has limited the scope of the project, approving an engineering study on just the first 11 miles, to Reston.

The metropolitan region is, by far, the largest market in contention for the Expos. The other contenders are Norfolk, Las Vegas, Portland, Ore., and Monterrey, Mexico.

With 7.6 million people in the metropolitan statistical area that includes Baltimore, the D.C. region represents the nation's eighth-largest media market. And it is one of the wealthiest in the nation.

Because the District lies at the heart of that market, D.C. officials argue that a downtown stadium would tap its fullest potential, drawing fans from across the region. On any given night, about 5 million people can get to downtown Washington within an hour and 15 minutes, according to statistics compiled by D.C. baseball boosters. Dulles boosters cast the issue differently, saying that when their stadium would open, 1.5 million people would live within an hour's drive at rush hour.

Population projections put together as part of the Dulles bid show swift population growth continuing near the ballpark site. By 2010, two years after the stadium's opening, 1.4 million people would live within a 10-mile radius of the stadium, and 2.3 million would live within 20 miles, according to those projections.

The District stadium would be located, at most, 20 blocks from the U.S. Capitol. Members of Congress, administration officials, law firms and lobbyists would flock to purchase season tickets and luxury skyboxes, according to city officials. And the view from the stands would be likely to include the Capitol dome, the Washington Monument or the Potomac River, giving the park a cachet no other city could match, they said.

"They're going to build a city around a stadium out there in the middle of nowhere when we have a city right here that already exists," Bullock said.

Laurence E. Bensignor, chairman of Diamond Lake Associates, a partnership of some of the nation's largest home builders that would build the development around the Loudoun stadium, said the Dulles location offered a chance to shake up the trend toward downtown stadiums. "What we're trying to do is marry the energy of an urban environment with the benefits and open space of suburbia," he said.

Some classic urban stadiums were born in gritty downtowns in the early 1900s, he said.

"Life isn't the same as it was 100 years ago," he said. "The automobile plays a different role today. Suburbia plays a different role today. We're looking forward."

"While there is a nice emotional feel to [Baltimore's] Camden Yards going back to the downtown, it would be naive to think that that is the only model, either experientially or financially," Bensignor said.

The wild card in all this is the role of Baltimore Orioles owner Peter Angelos. Angelos, a close ally of baseball Commissioner Bud Selig, has said repeatedly that a team in Washington, 35 miles from Camden Yards, would cut into his profits. D.C. officials argue that any harm to the Orioles could be mitigated by the formation of a regional cable sports network. But Angelos's opposition is a major stumbling block that could push the Expos into Northern Virginia -- or out of the region altogether.

Virginia baseball backers say the Loudoun bid could emerge as the compromise candidate, appeasing Angelos because it is farther from Baltimore but still able to tap the region's wealth.