Congressional officials announced today that the government plans to suspend the “cash for clunkers” program since concerns were raised that it could rapidly run out the $1 billion in rebates for new car purchases.

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 more fuel-efficient vehicle.

The congressional officials spoke on condition of anonymity because they were not authorized to speak publicly. A White House official later commented that officials were taking a closer look at the situation, but reassured auto dealers and consumers to have confidence that transactions under the program that already have taken place would be honored.