Washington » The U.S. government's Cash for Clunkers program has prompted so many buyers to trade in their old cars for new ones that some dealers say their lots are quickly thinning out.

Dealers say the bulk of the buyers want Toyotas and are trading in vehicles made by the Big Three American car makers. The government says nearly a quarter-million vehicles have been traded in.

"Inventories are running low," said Tammy Darvish, head of the Darcars auto chain, which has 28 dealerships in the Washington, D.C. region.

One of the problems, she said, is that General Motors and Chrysler shut down some of their plants over the spring and summer and are now just starting production lines back up. Toyota and other car makers had also scaled back their production levels. That's leaving some dealers without enough cars.

Kathy Graham, a spokeswoman for Chrysler, said 10 of the company's plants started up again July 27.

She said that the company's Jeep Compass, Jeep Patriot and Dodge Caliber are in short supply, but that dealers should start to see new deliveries in the coming weeks. Graham said the vehicles are in short supply because the clunker program started off with so much hype. Chrysler dealers had 2,000 people who were on a waiting list for vehicles before the program even officially started July 24.

Although running out of cars might be frustrating for consumers, Graham said it is exactly what Chrysler needed to streamline its vehicle supply. Dealers' inventories had piled up supplies of 100 to 120 days, which is too much when vehicle sales are down. Now, she said, they are averaging 45- to 60-day supplies in large part because of the clunker program.

"Now we're not just building to build," she said. "We're getting customer orders, we're getting dealer orders. That's the right thing for the company to do."

Toyota said it plans an increase of 75,000 vehicles. Of those Toyotas, 8,500 vehicles would come to the mid-Atlantic region, according to Darvish. But it will be several more weeks before she and other dealers see them on their lots.

Cash for Clunkers began July 24, with the government providing vouchers of either $3,500 or $4,500 for consumers who trade in old vehicles with low mileage for new fuel-efficient models.

Last week, as the $1 billion allotted to the program appeared in danger of running out, the Senate followed the House in approving another $2 billion for it.

Darvish said that although the government has improved the speed of its Web site where dealers have to file information about the trades, it has yet to pay them for the trade-ins they've accepted. That's left many dealers low on cash.

Darvish said she's owed nearly $3 million from the government for the clunkers she's taken in. "I haven't been paid the first penny," she said Tuesday morning. "There's no one to call. You get prerecorded messages," she said of the U.S. Transportation Department.

Some dealers say the program's popularity will soon wear off, but others don't think so and worry that the new batch of money won't last through Labor Day as officials from the Transportation Department had predicted.