Business leaders hoping to bring baseball to Loudoun County have been adamant in their proposal to major league officials: Baseball in Northern Virginia is so much more than a new home for the ailing Montreal Expos.

It's a 450-acre lakefront "new town" with office buildings, hotels and thousands of residences that they said will forge a new prototype in ballpark development and baseball economics and will be a boon to team owners and the region. They've dubbed their mix of commerce, scenery and box seats near Dulles International Airport "Virginia's Ballpark at Diamond Lake."

The problem is, the baseball backers don't own most of the land. Tax records and interviews with owners who control the majority of the property indicate that the developers have agreements to buy, at most, only about a third of it.

As baseball executives enter the final stages of their search for a new home for the Expos, it is unclear how the unsettled nature of the Diamond Lake project is affecting the closely held negotiations with Major League Baseball officials. The questions come at an especially sensitive moment in the years-long quest to return big-league baseball to the Washington area.

Major League Baseball is concentrating its search on four sites to move the Expos to for the 2005 season: the District, Northern Virginia, Las Vegas and Norfolk, according to senior league sources. The league has issued detailed legal and financial questionnaires to those bidders to evaluate the locations and get the clearest financial picture possible, the sources said. Those questionnaires are being completed and evaluated.

One source familiar with the negotiations between Virginia and baseball officials, as well as with talks over the past several years, said the effort has never reached this level of detailed legal negotiation. That source, who spoke on condition of anonymity because of the sensitivity of the negotiations, thought that the list had been narrowed further. "It's safe to assume that D.C. and [Northern] Virginia are the two finalists," the source said.

Representatives of the Virginia Baseball Stadium Authority, the state agency responsible for building a stadium if baseball executives decide to locate a team in the commonwealth, declined to comment on efforts to secure land. But Gabe Paul Jr., the authority's executive director, argued that the stadium could be built even without some planned amenities.

"Can you do Diamond Lake without the lake?" Paul said. "Yeah, sure you can."

Such an eventuality would mark a stunning rollback from the vision Paul and his fellow baseball boosters offered Major League Baseball executives in May. But the developers crafting the Diamond Lake project said they're veteran builders intimately familiar with the undulations and pitfalls associated with such a massive undertaking. They said they're not worried.

"It's what we do for a living," said Laurence E. Bensignor, chairman of Diamond Lake Associates LLC, a consortium of some of the nation's top home builders. "We have been working with the stadium authority and the county and landowners, and we have complete confidence in our ability to do not just a viable, but a successful, project."

Bensignor noted that Diamond Lake controls a site appropriate for the stadium. Builders need about 12 acres for the ballpark, he said.

"We have a site we believe will be the ultimate site, and we have it under contract. I'm not sure D.C. can say that, other than RFK" Stadium, Bensignor said.

The District, too, faces challenges in putting together the real estate for a stadium. Although the city controls Robert F. Kennedy Memorial Stadium and a second site is owned by the National Park Service, the remaining two sites are privately owned.

If nabbing a 12-acre stadium site in Loudoun County was tough, securing city blocks in the District for possible construction would be significantly harder, Virginia backers said.

Cobbling together the numerous parcels needed for the 450-acre Dulles development, however, has proved to be more difficult. The full extent of Diamond Lake's acquisitions remains unknown, and executives will not discuss their holdings.

But a representative of the family who runs Chantilly Crushed Stone, owners of more than 220 acres at the site -- including the quarry touted as the project's centerpiece -- said the company has not agreed to sell the property and is not in negotiations with the baseball developers.

Another key landowner said the same thing. "There are no negotiations on this issue so far," said Samir Kawar, an investor and former government minister in Jordan who owns 75 prime acres at the site. "I have received nothing serious."

Still, in a May letter to major league executives, Paul underscored the venture's success at assembling an attractive site.

"Let me tell you in confidence that most of the land parcels comprising this stunning 450-acre site are now under the control of the development group, including the property where the ballpark will sit," Paul wrote, according to a copy of the correspondence.

There are more than 50 parcels at the site, which is bordered by Route 28, the Dulles Toll Road, Old Ox Road and along Rock Hill Road and the Fairfax border. Combined, Kawar and Chantilly Crushed Stone own about two-thirds of the land but just 20 parcels, according to the latest Loudoun data. Bensignor would not say whether his group controls the majority of parcels. One landowner said the authority had given baseball executives a false impression, a contention Paul disputed.

"In any statements I've ever made, I don't think I've been deceptive at all," Paul said.

Diamond Lake representatives have negotiated sales agreements with many small land owners. Those sales are not yet completed and therefore not entered into the public record. None of the principals would discuss price.

Paul and Bensignor said their plan is to put the stadium north of the black glass Center for Innovative Technology, though the location could change.

That's the neighborhood where Edwin Bush's great-grandfather, a former slave, and his family have owned land since the late 19th century. Bush and more than a dozen other descendants reached an agreement with Leonard "Hobie" Mitchel, president of the Diamond Lake development group, to sell 20 acres, contingent on Loudoun's granting developers the zoning they request for a mixed-use development.

Bush said the push to transform the remnants of the small black community of Rock Hill into a flashy development leaves him divided. Although he likes the idea of cashing out and moving south, he said he also can't shake memories of his family's thwarted efforts to build on its land over the decades. Bureaucracy, land-use rules and perhaps racism were to blame for that earlier failure, which helped drive people away, he said.

"All this land out here used to be owned by blacks," Bush said. "It used to be a community. The older members died, and the younger folks wanted a better life, so they moved. I don't think they found it."

Bush said developers were initially coy about their intentions for the land. "They've been trying to keep us in the dark so we wouldn't hold out and make more money off it," he said.

His brother, Louis Bush, who had long ago moved to Newport Beach, Calif., and recently returned to help organize the sale, is less conflicted. "This would be a good building block for the growth in this area," Louis Bush said.

Spring saw a burst of offers on many of the small parcels in the area, with dueling bids pushing prices higher. Some property owners said they took lower bids from the Diamond Lake group because they trusted the financial heft behind the project's backers. Others were convinced by the group's assurances about the future.

"The buyer says they are pushing the whole corridor, regardless of whether baseball comes through or not," said Les Horowitz, a Reston computer programmer who reached an agreement to sell about four acres to Diamond Lake.

Asked whether he'd build Diamond Lake without the diamond, Bensignor demurred. "First things first," he said, adding that all his energy is spent trying to persuade Major League Baseball to move to Dulles. But it's a good idea either way, he said.

"Adding baseball creates a whole new dimension, but the concept of a town center is the right one anyhow," Bensignor said.

For Kawar, selling his prime corner property for a baseball development might be the way to close out an investment he made in America in 1979 on the advice of a real estate agent.

Or it might not.

Back then, developers passed on the land because they weren't sure about road connections. "I bought it and said, 'I'll leave it as security for my children,' " Kawar said.

He donated land to build Virginia's Center for Innovative Technology as part of a deal to ease his future building plans and spent years amassing the zoning permission and other preparations needed for a large commercial project.

Now, as push seems to be coming to shove, Kawar, who is chairman of the board of Middle East Insurance Co., said he'll be careful. He wants to be sure local and state officials are on board with the baseball development.

"There are a lot of people who are trying to fish and trying to make a buck like this. They like to be smart. They think they can make quick money on that. . . . I only talk, myself, to serious people," he said.

"Everything's up in the air, like hearsay," Kawar added. "I will get into the end result, that's all. . . . Then I don't mind. Then we will work out something."

Staff writers Thomas Heath, Lori Montgomery and Michael D. Shear contributed to this report.