Two sites proposed for a major league baseball stadium in Fairfax and Loudoun counties would face significant hurdles, according to political and community leaders who said lack of transportation tops their list of worries.

Virginia Baseball Stadium Authority officials proposed five locations for a stadium Saturday in case Northern Virginia wins a bid against the District and Portland, Ore., to land the Montreal Expos. Though Virginia baseball officials said they had no preferred site, much of the news conference centered on the three Arlington sites because of their views of Washington's monuments and access to existing transit stations.

One of the Fairfax sites straddles the Loudoun line, east of Dulles International Airport and next to the Center for Innovative Technology, a black odd-shaped building in Herndon. Access would be off the Dulles Toll Road, Routes 28 and 606, and Shaw and Rock Hill roads. A rail station is planned near there.

The other site is on surplus Army land near Fort Belvoir. Access would be off Interstate 95, the Fairfax County Parkway and Franconia Springfield Parkway. Metro's Blue Line would be extended from the Franconia Springfield Metro station.

Fairfax supervisors already voted once to drop the Fort Belvoir location and another one in Herndon in 1996 after residents complained. Not much has changed since then; the county supervisors who represent the Dulles site said Monday that Arlington is a better place for baseball in part because Metro is already there.

"I'm always open-minded, but it's not a promising location," said Loudoun Board of Supervisors Chairman Scott K. York (R-At Large) of the site near Dulles. "As a great baseball fan and [one who is] hopeful that it does come to Northern Virginia, the Arlington site is much better and more suitable. It has the rail stop near it, which is critical to its success, and is more central to the population itself."

Fairfax Supervisor Catherine M. Hudgins (D-Hunter Mill) said baseball would benefit the region "but I don't think the people of the Hunter Mill District and the Dulles corridor believe it belongs there."

Hudgins added, "Having a baseball stadium at a working and functioning transportation center is ideal. Arlington has it. D.C. has it."

The Arlington sites include property in Rosslyn, near the River Place apartment complex; Pentagon City, at the Costco complex next to the shopping mall; and another Pentagon City location on Army Navy Drive. Transit already is close by; neither the Dulles nor Springfield sites have existing rail stations. Arlington officials have cited their own concerns about a stadium there.

The Springfield site, at the old Engineer Proving Grounds, would be in an area already overwhelmed by local traffic, in part because of an expansion at Fort Belvoir. Supervisor T. Dana Kauffman (D-Lee) said Monday the Springfield site would be "out of step with community plans and public priorities."

He said stadium backers assume Metrorail would be extended. But that money would be far better spent, he said, extending the Blue Line to Fort Belvoir to support the installation and ease the burden on area commuters.

"It's something that would be used seven days a week, not just when baseball or a tractor pull is in town," Kauffman said.

Michael DeLoose, president of the West Springfield Civic Association, which represents more than 1,000 families, denounced the proposal as "incomprehensible . . . one that boggles the mind."

"Even among big baseball fans -- and I'm a big baseball fan -- the idea of putting a stadium [in Springfield] just doesn't make sense," DeLoose said. "And for folks who aren't baseball fans, they're looking at an extra 81 days or nights with a clogged Backlick Road and a clogged Mixing Bowl. . . . The proposal is just guaranteed to prompt the same reaction in the community as when [a baseball stadium] was considered in 1996 ."

The vote then among civic association members, DeLoose said, was 200 to 1 against.

Fairfax Supervisor Michael R. Frey (R-Sully), a member of the Virginia Stadium Authority, said Springfield residents should weigh the merits of a stadium against what is already planned for the now vacant area: 4.5 million square feet of office space and 2,000 residential units. A ballpark could actually be a catalyst to extend rail to the site, he said.

Public perception, he said, is one of the biggest obstacles facing the project in Northern Virginia, as people are visualizing the last generation of ballparks -- monolithic structures surrounded by a sea of parking.

But today's ballparks are different, he said, designed to be smaller, sleek entertainment complexes that fit cohesively into the landscape.

"There's been so much fear and so much NIMBYism," Frey said. "It's not unexpected that everyone is being cautious until they have the details and specifics. I expect any jurisdiction to be noncommittal" at this stage.

Today's ballparks are designed to be smaller and fit cohesively into the landscape, stadium defenders say.One proposed site for the ballpark straddles the Fairfax-Loudoun line, east of Dulles International Airport.Another proposed site is on surplus Army land near Fort Belvoir, accessible by Interstate 95, the Fairfax County Parkway and Franconia Springfield Parkway.