Aug. 5 (Bloomberg) -- A proposal to inject $2 billion into the “cash for clunkers” program has been delayed in the U.S. Senate by negotiations over whether to allow changes to the measure the House approved last week.

The Senate won’t vote today on the plan to extend the auto trade-in program through August, Senator Dick Durbin of Illinois, the second-ranking Democrat, said in an interview.

“We’re still waiting to hear from Republicans,” Durbin said. “They have a lot of amendments.”

Democrats were seeking an agreement to pass the measure without changes, because any alterations to the legislation the House passed July 31 would force a suspension in the program until the House could vote on the revisions when it returns from a monthlong recess Sept. 8.

“We can’t allow this bill to be amended,” said Jim Manley, a spokesman for Senate Majority Leader Harry Reid.

The government’s Car Allowance Rebate System provides credits of as much as $4,500 for the purchase of a new, more fuel-efficient vehicle when buyers turn in an older car or truck to be junked.

Reid, a Nevada Democrat, said he expects to reach an accord with Republicans that would allow the Senate to approve the money this week. If no agreement on timing is reached, Reid said he will try to pass a procedural motion that would force a final vote over this weekend.

Reid said today there is “a significant majority” of senators who want to extend the program, which ran through about $1 billion in its first week while boosting auto sales nationwide.

Time Limit

Some Republican senators want to alter the legislation passed by the House last week to set a time limit on the program.

“There is a belief this will continue to grow and grow and grow and $2 billion may not be enough” unless limits are imposed, Senator John Thune, a South Dakota Republican, told reporters.

Republican leader Mitch McConnell, a Kentucky Republican, said yesterday the Senate will vote on the proposal “before the end of the week.”

Automakers and dealers are pushing the Senate to pass the measure, saying the program is a success. Ford Motor Co., the only major U.S. automaker that hasn’t received direct U.S. government aid, posted its first monthly sales gain since 2007 in July, the month the clunkers program began.

Ford Focus

Ford’s Focus was the top seller so far under the program, followed by Toyota Motor Corp.’s Corolla, Honda Motor Co.’s Civic and Toyota’s Prius and Camry, data from the Transportation Department showed this week.

The Transportation Department had received about 157,000 dealer applications for funds totaling $664 million, as the agency works through a backlog that reached hundreds of thousands of online submissions, Transportation Secretary Ray LaHood told reporters yesterday.

Vehicles made by the three largest U.S. automakers -- General Motors Co., Ford and Chrysler Group LLC -- comprised fewer than half of sales under the program through Aug. 1, according to the Transportation Department data obtained Aug. 3. The companies accounted for 47 percent of the clunkers transactions.

The data didn’t break out where the cars sold were manufactured. Some vehicles sold by foreign companies are manufactured in the U.S.

To contact the reporters on this story: Angela Greiling Keane in Washington at agreilingkea@bloomberg.net; Holly Rosenkrantz in Washington at hrosenkrantz@bloomberg.net

Last Updated: August 5, 2009 15:48 EDT