But a White House spokesman said later the Obama administration is "evaluating all options" to keep the program funded and that all valid deals made so far will be honored.

Under the program, which began last Friday, consumers were able to trade in older vehicles with fuel-economy ratings of 18 miles per gallon or less for vouchers of either $3,500 or $4,500 toward the purchase of a new vehicle that gets better mileage.

Transportation Department officials called lawmakers’ offices earlier Thursday to alert them of plans to suspend the program as early as today. But the White House said later the program had not been suspended.

"We are working tonight to assess the situation facing what is obviously an incredibly popular program," White House press secretary Robert Gibbs said.

The National Highway Traffic Safety Administration, which is administering the program, reported at the close of business Thursday afternoon that only about $95 million of the money had been approved for payment to dealers.

But NADA Chairman John McEleney, a Clinton, Iowa, General Motors/Toyota/Hyundai dealer, said that a poll of about 2,000 of the group’s 23,000-plus dealers showed that with deals already in the works, it was probable that the rest of the $1 billion was already tied up in transactions that had not been submitted or approved by the government.

The Safety Administration said earlier in the day that the vast majority of applications submitted by dealers were being rejected because of incomplete or illegible paperwork, but it was expected that those transactions eventually would be submitted properly and would receive the government money.

Sen. Debbie Stabenow, D-Mich., said late Thursday that lawmakers had been informed of the government’s decision to suspend the program.

"It is amazing that ‘Cash for Clunkers’ would be this successful this quickly," she said in a statement. "I urge Congress and the administration to provide additional funding."

The Transportation Department called Congress members to alert them to the decision to suspend the program.

Congress last month approved the Car Allowance Rebate System, the official name of the clunkers program, to boost sagging auto sales and remove some vehicles with poor fuel economy from the roads.

Officially, the program began July 1, but dealers were not able to begin submitting paperwork to recover the rebates from the government until last Friday afternoon, when final rules were published.

Because some dealers nationwide actually began delivering vehicles under the program as early as July 1, there is "a significant backlog of … deals that make us question how much funding is still available in the program," NADA spokesman Bailey Wood said.

Even before the suspension announcement, some in Congress were seeking more money for the program.

Rep. Candice Miller, R-Mich., wrote a letter to House leaders requesting additional money.

"This is simply the most stimulative $1 billion the federal government has spent during the entire economic downturn," Miller said. "The federal government must come up with more money, immediately, to keep this program going."

General Motors spokesman Greg Martin said Thursday the automaker hopes "there’s a will and way to keep the CARS program going a little bit longer."

Dealers had already reported, however, that many consumers who wanted to use the clunkers program did not have eligible vehicles. Dealers said many customers were buying cars anyway, which was one of the intended benefits of the program – getting people into showrooms that had been mostly vacant for the past year.

So far this year, through June, U.S. new-vehicle sales had fallen about 35%, to an annual level of fewer than 10 million vehicles. That compares with 2007’s record year of about 16.3 million new vehicles sold. (Tire Review/Akron)