The Transportation Department called lawmakers' offices to alert them to the decision to suspend the program at midnight Thursday. The program offers owners of old cars and trucks $3,500 or $4,500 toward a new, more fuel-efficient vehicle.
The congressional officials spoke on condition of anonymity because they were not authorized to speak publicly.
A White House official said later that officials were assessing the situation facing the popular program, but auto dealers and consumers should have confidence that transactions under the program that already have taken place would be honored.
Rae Tyson, a spokesman for the National Highway Traffic Safety Administration, which administers the program, declined comment.
Congress last month approved the Car Allowance Rebate System program, known as CARS, to boost auto sales and remove some inefficient cars and trucks from the roads. The program kicked off last Friday and was heavily publicized by car companies and auto dealers.
Through late Wednesday, 22,782 vehicles had been purchased through the program and nearly $96 million had been spent. But dealers raised concerns about large backlogs in the processing of the deals in the government system, prompting the suspension.
A survey of 2,000 dealers by the National Automobile Dealers Association found about 25,000 deals had not yet been approved by NHTSA, or nearly 13 trades per store. It raised concerns that with about 23,000 dealers taking part in the program, auto dealers might already have surpassed the 250,000 vehicle sales funded by the $1 billion program.
"There's a significant backlog of 'cash for clunkers' deals that make us question how much funding is still available in the program," said Bailey Wood, a spokesman for the dealers association.
Even before the suspension, some in Congress were seeking more money for the auto sales stimulus. Rep. Candice Miller, R-Mich., wrote in a letter to House leaders on Wednesday requesting additional funding for the program.
"This is simply the most stimulative $1 billion the federal government has spent during the entire economic downturn," Ms. Miller said Thursday. "The federal government must come up with more money, immediately, to keep this program going."
THE PROGRAM: The federal Car Allowance Rebate System offered rebates of $3,500 to $4,500 for car shoppers who scrapped their old vehicles to buy ones with better gas mileage. The program, which began last Friday, was expected to run through Nov. 1 or until the $1 billion stimulus ran out.
THE RESPONSE: Through late Wednesday, 22,782 vehicles had been purchased and nearly $96 million had been spent.
THE PROBLEM: A survey of 2,000 dealers by the National Automobile Dealers Association found about 25,000 deals not yet approved by National Highway Traffic Safety Administration. With 23,005 dealers asking to participate, auto dealers might have already arranged the sale of more than the 250,000 vehicles that federal officials expected the plan to generate.