Loudoun County officials are willing to hand over hundreds of millions of dollars to build a baseball stadium and subsidize team owners if Major League Baseball moves the Montreal Expos to a site beside Dulles International Airport, backers of Virginia's bid said.

Revenue from a proposed Loudoun tax on game tickets and an array of county tax breaks are central to Virginia's financing plan. But they have been discussed little in public, and officials said they cannot put a dollar amount on the benefits Loudoun would receive in return.

With league officials' decision on where to put the Expos expected soon, the upsides baseball would bring to Loudoun -- and the price it would exact from the county -- are getting new scrutiny from boosters and critics.

Bruce E. Tulloch (R-Potomac), vice chairman of Loudoun's Board of Supervisors, said the ballpark would be an engine -- "quite frankly, a Ferrari," he said -- for the county's economy. It would create jobs, attract businesses and spur residential construction near the stadium, all of which would pump up county finances, he said.

But Supervisor James Burton (I-Blue Ridge) predicted that the economic development benefits of hosting a major league team would prove insignificant, and he said siphoning off tax proceeds collected by the county to fund the ballpark's construction would undermine the stadium's value to Loudoun taxpayers.

The struggle over Virginia's stadium financing plan, and Loudoun's role in it, is about more than baseball. At issue is just what role governments should play in subsidizing the private keepers of the nation's pastime.

That question is especially relevant in Loudoun, which, as the nation's fastest-growing county, has been wrestling with growth and rising tax bills. It is also a central issue in the District, where voters in last week's Democratic primary threw their weight behind three D.C. Council candidates who, given other pressing city needs, opposed public financing for a ballpark.

Virginia's stadium plan counts on Loudoun supervisors to impose a 10 percent ballpark admissions tax, then pass the more than $300 million in expected revenue over 30 years to the Virginia Baseball Stadium Authority. The county also would hand over admissions taxes on events other than baseball games at the park and give the authority local sales tax revenue from stadium spending, according to the authority, which was created by the General Assembly to lure a team and finance and build a ballpark.

Team owners would get 40 percent of whatever's left after the authority covers its yearly debt payments and other stadium costs.

The county also would forgo property taxes on the $360 million ballpark, home to what would become one of the county's largest private employers, according to the plan.

Academic experts who study the impact of stadiums on communities said proponents of public investments -- whether via government grants, tax pass-through arrangements or other special tax agreements -- dramatically overstate the payback residents can count on from big-time sports complexes.

The D.C. Sports and Entertainment Commission has argued that a new downtown stadium would generate 2,100 jobs. An analysis commissioned by supporters of Virginia's bid and performed by George Mason University professor Stephen S. Fuller, meanwhile, says a ballpark would produce 2,671 jobs.

Andrew Zimbalist, a Smith College economics professor, said independent studies show that stadiums are generally a wash.

"You shouldn't expect any job creation at all," Zimbalist said. "You should expect an economically neutral outcome." He added that while some places might see a slight positive impact, others could see a decline.

Zimbalist said there are social and cultural arguments for why the public should invest in a ballpark. But, he said, "anyone who says you should do this because it will be the cat's meow for economic development should not be trusted."

And the promised benefits are not always as rosy as they initially seem, said Ed Lazere, executive director of the D.C. Fiscal Policy Institute. Lazere said city figures show that only several hundred of the jobs that a ballpark would create would go to District residents, and it remains unclear whether others could lose their jobs elsewhere in the city.

"In general, all the results are suspect," he said.

Among baseball's most fervent boosters, that's sacrilege.

"How can that be anything but an economic gain and huge psychological gain for Loudoun County?" asked Keith Frederick, chairman of the stadium authority. "That's what economic development is, isn't it, bringing in money and jobs?"

Johns Hopkins University economist Bruce Hamilton sees the cons generally canceling out the pros.

"All you're doing is reshuffling money that would have been spent in the Washington area anyway, probably on an entertainment venue," Hamilton said. "Basically, the only thing a baseball stadium can do is redistribute the revenues from bowling alleys to baseball games, and that's a zero sum."

In a meeting Tuesday, Virginia's baseball boosters continued to try to convince representatives of Major League Baseball that all the Loudoun, state and other revenue they say they have lined up would not only cover construction but also pour huge sums into the pockets of the Montreal Expos' new owners.

They also touted a series of what they said were good alternatives to using Virginia's moral obligation to finance much of the ballpark, given the continuing concerns of Gov. Mark R. Warner (D) and key legislators.

Among the possibilities: replacing bonds with loans or other private financing, or using public institutions, such as a local industrial development authority.

The enthusiastic tax breaks envisioned in Loudoun come in sharp contrast to the denunciations Loudoun's Republican supervisors directed toward health researchers at the nonprofit Howard Hughes Medical Institute this year for tax breaks on their major science facility, demonstrating how the aura of baseball can alter political calculations.

Tulloch, who as leader of the GOP majority on the county board has led the baseball talks, said it is premature to comment on some of the specifics of Loudoun's tax plans for the stadium because league officials are still picking them over to choose their preferred package. Tulloch declined to call the 10 percent stadium admissions tax a tax, saying he prefers the term "user's fee."

Tulloch said a Major League Baseball official indicated last week that the county was still being considered, despite the District's marathon meeting with baseball officials on details of a possible Expos move to the city.

According to Fuller, Loudoun's investment would bring hefty dividends. The major league team and the stadium would result in about $2 million in additional revenue for Loudoun County in a typical year, he said. Depending on the size of the proposed adjoining commercial and residential development, Fuller added, those figures could be dramatically increased.

Fuller argued that the stadium could lure the kind of high-quality businesses and development that characterize Loudoun's populous and wealthy neighbor to the east, Fairfax County.

"Loudoun is struggling to find its identity. It wants to grow up like its big brother, and this helps jump-start that," Fuller said.

Burton said he's waiting to see the details before deciding how he would cast his vote, though support for baseball is strong on the board either way.

"I just love baseball, but I don't see an economic benefit to the county," Burton said. "Why would somebody want to move to Loudoun County simply because there's a baseball stadium there, when they could just watch the game at night on cable without dealing with the traffic and the congestion?"