President Obama recently signed a $2 billion extension of the original $1 billion program to support a total of 750,000 trade-ins before the money runs out in the next few weeks, depending on how fast consumers snap up the offer.

As the $3,500 to $4,500 subsidy continues, unintended side effects have begun to emerge, creating winners and losers even among new car buyers.

"The clunkers program has been like a double-edged sword," said analyst Jessica Caldwell of Edmunds.com, a Web site in Santa Monica that tracks car sales.

"It gave new car dealers some excitement and gave the whole auto industry a jump start," said Caldwell. But she said the sudden demand also put some models in short supply and probably made dealers less likely to discount.

"People who are going in to buy new cars now who do not have a clunker could be paying more money," she said.

Nonprofit groups that raise money by accepting donations of older vehicles have been among the program's unintended losers. Vehicle Donation to Any Charity, a Point Richmond firm that works with 4,500 nonprofits nationwide, recently said its intake of old cars has dropped 20 percent since the program went into effect.

Used car dealers have been particularly irate about the subsidy, saying it has driven buyers to new car lots at a time when their business was already suffering from tight credit and a shortage of used cars.

"Before the clunkers, business had been off at least 30 percent from last year, and after the clunkers started it fell another 20 percent," said Sevki Abbasoglu, owner of the Auto Exchange used car lot in Alamo.

"This is completely unjust," said Terry Degmetich, a used car dealer in Roseville and president of the Independent Automobile Dealers Association of California.

The program was defended by Paul Taylor, chief economist with the National Automobile Dealers Association, which represents new car sellers.

"The government is getting what it wanted," Taylor said. "It's a stimulus program that gets immediate traction."

Taylor noted that Ford, Toyota, Chrysler and General Motors have all added production to replenish depleted inventories. Locally, New United Motor Manufacturing Inc., the Fremont auto plant whose future is in doubt, has said demand created by the clunkers program would keep the factory busy through October.

Even with the subsidy, Taylor said new car sales as of July were only on track to approach 10.4 million units in 2009, far below last year's 13.2 million.

Art Spinella, who follows used cars for CNW Marketing Research in Oregon, said despite any setback from the clunkers program, he projects that independent dealers will sell about 13 million vehicles this year, up from 11.7 million in 2008, as the recession steers buyers toward pre-owned cars.

Spinella said one unintended beneficiary of the program could be the private parties who sell about two-thirds of all cars 10 years old or older.

"They'll probably do better because the supply is shorter," he said. "But some consumer is going to pay a higher price either for the same year vehicle or by being forced to buy a newer vehicle."

What happens after the program ends remains a question mark.

Caldwell, of Edmunds.com, said the subsidy may have moved new car sales into the summer at the expense of the fall. "There may not be a turnaround in the marketplace, because in October sales could go back down," she said.

Taylor, with the Auto Dealers Association, said there has probably been a mix of sales pulled forward and sales inspired solely by the subsidy, but either way it was welcome.

"Dealers have been through a difficult cash flow period, and without this help some of them may not survive," he said.

For details about the Cash for Clunkers program, visit www.cars.gov.

E-mail Tom Abate at tabate@sfchronicle.com

This article appeared on page DC - 1 of the San Francisco Chronicle