MILWAUKEE — Robert Miranda worries about how the Cash for Clunkers program will affect social-service agency Esperanza Unida.

His organization uses donated vehicles to raise funds for its programs, and he is concerned that cars traded in as clunkers will end up in scrap yards instead of his facility.

He is not alone, as charitable organizations nationwide are carefully watching what impact the program will have on used-vehicle donations that fund major parts of their operations.

Officially known as the Car Allowance Rebate System, or CARS, the program offers consumers taxpayer-funded rebates of $3,500 or $4,500 for trading in older vehicles for new, more fuel-efficient models.

According to The Associated Press, the program has generated more than 435,000 vehicle sales and helped the U.S. auto industry emerge — at least partially — from its worst downturn ever.

Cars that are traded under the program must be destroyed, although some parts can be salvaged.

The auto repair program at Esperanza Unida in Milwaukee provides needy central city residents the opportunity to train in auto mechanics and also provides some city residents an affordable ride to work, Miranda said.

"We have seen a drop-off in quality used car donations," he said. "I'm keeping a close eye on it."

The agency accepts vehicle donations and makes them available based on an individual's need. Donors are eligible for a federal tax deduction.

"We could definitely use those cars," he said of the vehicles being destroyed under the clunkers program.

Many charity operators and economic observers say it's too soon to determine how the clunkers program will ultimately affect giving.

"It is logical that many charities would be hurt," said John List, an economics professor at the University of Chicago who has studied fund raising.

The National Kidney Foundation receives about 30,000 vehicle donations a year nationwide, accounting for 19 percent of the charity's total revenue.

Chad Iseman, director of the Kidney Cars program for the New York-based foundation, estimates a 10 percent to 15 percent decline in vehicle donations because of federal rebates.

"It is significantly impacting us," Iseman said. "We're just waiting for it to run its course."