DETROIT -- Congress could begin to debate an extension of the approved cash-for-guzzlers program as early as this fall if the current program proves to be a success, said Dave McCurdy, president of the Alliance of Automobile Manufacturers.

The program's $1 billion in funding is estimated to cover 250,000 vehicles. "I think it'll go very quickly, and Congress may have to revisit it in the fall," McCurdy told Automotive News today.

He said that "250,000 vehicles isn't enough."

"We think there'll be additional phases of this," McCurdy said. "It'll probably evolve."

The government is working out details of the cash-for-guzzlers program, which President Barack Obama signed into law on June 24. Those details have to be in place within 30 days, at which point the program will begin.

To get further funding, though, "it's important we show results early and very accurate results," McCurdy said.

In the Senate, he said, supporters of an extension will be "looking at different requirements," including perhaps a greater improvement in fuel efficiency before buyers qualify for the program.

Under the current program, a truck buyer qualifies for a $3,500 government credit if the qualifying new truck he or she buys delivers a combined city/highway fuel-economy improvement of at least 2 mpg beyond the vehicle traded in. For a car buyer to qualify for the $3,500 credit, the qualifying new car has to yield an improvement of at least 4 mpg. For larger improvements in fuel efficiency, the credit can jump to $4,500.

That car-truck discrepancy has led some to predict that the program will be used overwhelmingly for purchases of new pickup trucks. But McCurdy warned against that. Congress won't extend the program, he said, "if it's just a truck program for people buying F-150" pickups.