GREENBRIER COUNTY, W.Va. -- Workers atop mountain ridges are putting together 389-foot windmills with massive blades that will turn Appalachian breezes into energy. Retiree David Cowan is fighting to stop them.

Because of the bats.

Cowan, 72, a longtime caving fanatic who grew to love bats as he slithered through tunnels from Maine to Maui, is asking a federal judge in Maryland to halt construction of the Beech Ridge wind farm. The lawsuit pits Chicago-based Invenergy Wind LLC, a company that produces green energy, against environmentalists who say the price to nature is too great.

It is a rare green vs. green case, and it's scheduled to go to trial Wednesday in U.S. District Court in Greenbelt.

It is the first court challenge to wind power under the Endangered Species Act, lawyers on both sides say. With President Obama's goal of doubling renewable energy production by 2012, wind and solar farms are rapidly expanding. As they do, battles are being waged to reach the right balance between the benefits of clean energy and the impact on birds, bats and even the water supply.

At the heart of the Beech Ridge case is the Indiana bat, a brownish gray creature that weighs about as much as three pennies and, wings outstretched, measures about 8 inches. A 2005 estimate concluded there were about 457,000 of them, half the number as when they were first listed as endangered in 1967.

"Everything in life, including energy, involves tradeoffs," said John D. Echeverria, a Vermont Law School professor who specializes in environmental law and isn't involved in the lawsuit. "Any kind of energy development is going to have environmental impacts that are going to concern somebody. This has been an issue for the environmental community. They are enthusiastic; at the same time they realize there are these adverse impacts."

Both sides agree that Indiana bats hibernate in limestone caves within several miles of the wind farm, set in a lush, rural area where coal and timber industries once dominated. The question before the judge: Would the endangered bats fly in the path of the 122 turbines that will be built along a 23-mile stretch of mountaintop?

Cowan and other plaintiffs, including the D.C.-based Animal Welfare Institute, support wind power as one way to help mitigate climate change. But they say this setting is the wrong place for the massive turbines.

They argue Beech Ridge would kill thousands of bats -- about 6,700 each year -- and that Indiana bats will be among them. The Indiana bats, they contend, are likely to fly near the turbines in the fall as they migrate to caves from forests where they spend the spring and summer. Some biologists who analyzed recordings at the site say they are nearly certain that some of the calls were made by Indiana bats.

Any deaths would be a blow to a species that has been slow to rebound from the damage caused by pollution and human disturbance of their caves, partly because females have only one baby each year, the plaintiffs say.

"This case is not a referendum on wind power and its societal utility," said William S. Eubanks II, an attorney for the plaintiffs. "It is a challenge to a particular wind power project that will operate in an environmentally unsustainable manner by killing tens of thousands of bats, including endangered Indiana bats." He said Invenergy has not sought a permit under the Endangered Species Act that would set out conditions to lessen the likelihood bats would be killed.

Invenergy argues there is no sign that Indiana bats come to the ridge. When a consultant put up nets at or near the site in the summer of 2005 and 2006 to search for bats, no Indiana bats were captured. Some bat experts say the females prefer lower areas when they have their young, and the ridge is simply too high. The company also stresses that there is not a single confirmed killing of an Indiana bat at any wind farm nationwide.

"There is no reliable evidence that the bats use, migrate over, feed, breed or raise their young on the ridgeline where the turbines are located," said Kirsten L. Nathanson, an attorney at Crowell & Moring law firm, which represents the wind farm. "No one really knows where they go when they leave those caves in the spring, and there is no basis to believe they will pick Beech Ridge over tens of thousands of acres of suitable habitat in the surrounding region."

In an area scarred by mountaintop coal mining, company officials say the wind farm is a friend to the environment. The project would supply energy to an estimated 50,000 households. It also is bringing jobs to the region.

"We're a clean, green energy company," said Joseph Condo, vice president and general counsel. "The project will be able to deliver clean energy for years."

The $300 million project has twice survived challenges in the West Virginia Supreme Court, including complaints that it would mar the picturesque view. If the court does not intervene, the first set of 67 turbines are expected to be up and running next year. The state has required that bat and bird fatalities be tracked for three years.

The case likely will come down to a battle of bat experts.

There is no question that turbines in other locations have killed tens of thousands of bats. Some strike the blades. Others die from a condition known as barotrauma, similar to the bends that afflict divers. It occurs when the swirl of the blades creates low-pressure zones that cause the bats' tiny lungs to hemorrhage. Scientists and the industry are in search of ways to lessen the kills, including stopping the turbines during certain times, or using sound to deter the bats.

But the habits of Indiana bats largely remain a mystery to scientists. They are so small that only recently has the technology been available to produce devices small enough to track their movements.

Brad Tuckwiller, a county commissioner who manages his family's 1,700-acre cattle farm not far from the ridge, is a supporter of the wind farm. When the project was first proposed, he visited one of Invenergy's farms in Tennessee.

"I know some of our citizens are upset but I don't think it's about the bats. I think it's about the viewshed or fear," Tuckwiller said. "If America is going to have energy independence we have to look at these alternative sources -- solar, wind, geothermal, in addition to nuclear and coal."

To Cowan, the risk is simply too great. The house he and his wife built to be near West Virginia's caves has bat profiles on the windows. The wicker napkin holder on the dining room table is decorated with a bat. Their car has a bat bumper sticker.

"I think if the turbines kill one Indiana bat that ought to end it," he said. "That ought to shut it down."