Business leaders and officials hoping to lure the Montreal Expos to Northern Virginia gave Loudoun County representatives a private briefing yesterday on plans for a Major League ballpark and a large lakeside development at a quarry near Dulles International Airport.

Top officials from the Virginia Baseball Stadium Authority, prospective team owners and members of Diamond Lake Development outlined a proposal for 5 million square feet of commercial space and thousands of condominiums and apartments on about 400 acres near a proposed Metro stop, said Loudoun County Board of Supervisors Chairman Scott K. York (I), who added that some details are not determined.

York said he and Supervisor Bruce E. Tulloch (R-Potomac), who also attended the briefing, asked the development team to make a more complete presentation to the public within a month that would allow residents and county staff to analyze the financial and traffic effects of the proposal.

"I've seen the financing plan and the speculation on some of the numbers," York said. "If you take it on straight face value, there's some intrigue and some concern."

Leaders across the county's political spectrum said they would work to smooth the way for the ballpark as long as no local taxpayer money is needed -- as the developers have promised.

Supervisor James Burton (I-Blue Ridge), who has fought numerous development projects in the nation's fastest growing county, said he'd probably support this one.

"If they work up the necessary funding on their own, great. I wish them well," said Burton, who added that previous stadium proposals had foundered because they relied on taxpayers to underwrite increasingly costly venues. "That's always been one of the hang-ups in the past because the stadiums have gotten so expensive."

Loudoun Planning Commission Chairman Lawrence S. Beerman II said the proposed site -- northeast of the Dulles Toll Road and Route 28 -- is especially suitable because it sits in a commercial area where significant business growth already was contemplated and yet is near enough to large population centers to lure fans and year-round customers.

"You're accessible to the dollars you want to be accessible to, but you're not in anybody's back yard," Beerman said.

It was exactly those types of neighborhood concerns that thwarted efforts to locate a stadium in Arlington, which was one of a handful of possible Northern Virginia sites the Virginia Baseball Stadium Authority proposed last year. Fairfax and Prince William counties also have been considered.

The Dulles site emerged publicly in recent days as a top contender.

Jerry Burkot, an executive with the group of prospective owners vying to bring a team to Northern Virginia, said the group would prefer the Dulles site because it is in the heart of a fast-growing and wealthy area and offers a large enough space for the type of broader development that could reduce construction costs and make the venue a real "destination."

But Burkot noted that Major League Baseball makes the ultimate decision on where a team goes.

The District, Norfolk, Las Vegas and Monterrey, Mexico, are among those in the running. The District and Northern Virginia face sharp opposition from Baltimore Orioles owner Peter Angelos, who has argued that those locations are too close to Camden Yards and would draw fans away from his team.

Will Somerindyke, who represents the prospective owners in Norfolk, said his group's bid for the team solves the Angelos problem by being farther away -- "It makes it happy," he said -- and offers Major League Baseball the most attractive ballpark deal because public financing would cover the project.

"You have a fully funded stadium on city-owned property -- waterfront," Somerindyke said. "We don't have to worry about development or anything else. We have all the pieces."

The Dulles stadium financing plan envisions up to one-third of the ballpark's construction costs being covered by the ownership group through lease payments over 30 years. The rest would be covered by tax revenue generated in connection with the stadium, Burkot said. Burkot declined to comment on other bids or how the Dulles stadium financing plan stacks up.

Virginia Secretary of Commerce and Trade Michael J. Schewel said a team in Northern Virginia or Hampton Roads would provide an economic boost to the state and help shape a distinct identity in places that "have sort of a diffuse presence."

"It would be a good thing in terms of creating a business identity for the communities and attracting additional businesses," Schewel said.