ALAMEDA COUNTY, Calif. -- The long hot summers of the San Joaquin Valley suck great tsunamis of cool coastal air through the Altamont Pass, producing winds so powerful that a person can lean nearly 45 degrees without falling down.

Such awesome force gave birth in the early 1980s to the world's largest collection of wind turbines, pioneers in what is now America's fastest-growing form of renewable energy and an increasingly important weapon in the battle against global warming.

But the Altamont Pass Wind Resource Area is also a symbol of the wind industry's biggest stain -- the killings of thousands of birds, including majestic golden eagles, by turbines. The result has been a wrenching civil war among those who are otherwise united in the struggle to save the planet and its creatures.

It's been nearly a year since a controversial legal settlement was forged among wildlife groups, wind companies and Alameda County regulators. That agreement, opposed by some parties to the dispute, promised to reduce deaths of golden eagles and three other raptor species by 50 percent in three years and called for the shutdown or relocation of the 300 or so most lethal of the approximately 5,000 windmills at Altamont.

But five scientists appointed by the county say the settlement and accompanying efforts to reduce bird deaths are not on track to meet the 50 percent goal, and they recently surveyed the Altamont to determine which additional turbines should be removed or relocated to spots less likely to kill birds.

Known officially as the Scientific Review Committee, the panel agreed Dec. 21 that more turbines need to be removed or relocated. It issued a new list of 309 targeted turbines, plus 102 more if the wind companies refuse to continue a current, temporary shutdown of all their windmills into February. The wind operators had previously agreed to a two-month shutdown, for November and December.

FPL Energy, the company with the most turbines in the Altamont, has not seen the specifics of the new recommendations from the scientists and cannot comment, company spokesman Steven Stengel said last week.

"We are deeply distressed about the continuing bird deaths and about the companies not being on track for the 50 percent reduction," said Elizabeth Murdock, executive director of the Golden Gate Audubon Society, a chief plaintiff in the lawsuit that has reshaped the battle over the birds.

But Stengel said, "It is too early in the process to accurately judge whether we are on track." The scientific review is meant to find ways of protecting the birds without putting the companies out of business, he said.

No one knows for sure how many birds are killed by the Altamont turbines -- a 2004 California Energy Commission report estimated the golden eagle toll to be between 75 and 116 a year, while total bird kills were put in the 1,766 to 4,721 range. The Audubon Society lawsuit targets four raptor species -- golden eagle, red-tailed hawk, American kestrel and burrowing owl -- which suffered 456 to 1,129 fatalities per year, the study estimated.

Subsequent data indicate that bird deaths have not decreased since the settlement was reached last January and that efforts to achieve a 50 percent reduction in three years are far behind, said Shawn Smallwood, an independent consultant in avian ecology who co-authored the 2004 California Energy Commission study and is one of the five county-appointed scientists.

James Walker, president-elect of the industry-backed American Wind Energy Association, said the wind companies also want to save birds and are helping to fund the study of the problem. He also said wind power helps save bird lives by combatting global warming, which the National Audubon Society acknowledges as a threat to many bird species.

Rick Koebbe, head of Altamont Winds Inc., another of the half-dozen firms that own turbines in the Altamont, said the impact on birds has to be weighed against the human deaths and diseases that are reduced by using wind power instead of pollution-producing fossil fuels.

Numerous surveys and studies of dead birds have taken place in the Altamont going back to at least 1992, but the analysis, according to a 2005 Government Accountability Office review of the studies, "has been complicated by confounding variables."

The problem is not simply birds running into spinning blades. Many dead birds have been found around turbines that were turned off. Some have been electrocuted by live wires near operating turbines, while others apparently were killed by predators.

Despite the perplexing data, many experts agree that a chief cause of bird deaths is the sheer number of windmills at Altamont, which features many old, small turbines in the 100-kilowatt range. More modern wind farms employ taller, more powerful machines able to generate 1 to 3 megawatts.

Replacing the many old turbines with fewer, more powerful ones -- a process termed "repowering" -- is official county policy and would be "a big part of the solution," Murdock said. The idea is that bigger turbines would not only dramatically reduce the spinning blades to about one-tenth of their current number but also turn more slowly and be higher off the ground, presumably moving them farther away from raptors that dive for mice and other prey.