WASHINGTON  – The Senate is poised to add $2 billion to the popular “cash-for-clunkers” program after lawmakers agreed to vote on the government car incentives and give shoppers until Labor Day to make a deal on more energy-efficient models.

The White House has estimated that tripling the $1 billion program could pay for 500,000 more new-car sales, giving automakers a late-summer boost after months of ragged business. The Obama administration has said the program would go broke by Friday without Congress’ approval of the extension.

Senate Majority Leader Harry Reid said Democrats and Republicans had agreed to vote on the plan later Thursday after the formality of considering potential changes to the House-passed version of the bill. None of those amendments is expected to pass.

Senate approval of the House version would send the legislation to the White House for President Barack Obama’s signature and assure consumers there will be no interruption in the program that provides up to $4,500 in rebates and helped rescue car dealerships from lagging sales.

“There’s a significant majority that want to move forward with this legislation,” said Reid, D-Nev., who nonetheless agreed to bring up amendments as a goodwill gesture to those who otherwise might try to delay a final vote on the House-passed version.

The proposed changes that will receive an airing include placing an income limit on those benefiting from the vouchers, terminating the Troubled Asset Relief Program and requiring the government to sell off its shares in Michigan automakers General Motors Co. and Chrysler Group LLC.

Sen. Tom Harkin, D-Iowa, for example, wants the vouchers limited to individuals earning less than $50,000 a year or joint filers earning less than $75,000.

As the bill stands, Microsoft founder Bill Gates can get $4,500 to buy a new car, Harkin said Thursday. “You have to ask,” Harkin said, “is this a wise way to spend limited amounts of money?”

Any Senate changes to the bill would require another vote in the House, something that couldn’t take place until the House returns in September from a monthlong recess. The Senate is taking its break following votes on the car incentives and the confirmation on Supreme Court nominee Sonia Sotomayor.

Republican opponents have conceded they are unable to force all of the changes they want or to block the House version of the bill. But they still grumbled about more government handouts to the private sector.

Sen. John Thune, R-S.D., called the bill an example of “Congress choosing winners and losers among industries.”

The government said Wednesday that more than $775 million of the $1 billion fund had been spent, accounting for nearly 185,000 new vehicles sold. Administration officials estimate the extra funding will last into Labor Day.

Car companies credit the clunkers program with driving up sales. Most consumers are buying smaller, more fuel-efficient vehicles through the program, according to a list of the top-10 selling cars released by the government.

Among manufacturers, General Motors Co. had the largest share, accounting for 18.7 percent of new sales; followed by Toyota Motor Corp., with 17.9 percent; and Ford Motor Co., with 16 percent. Detroit automakers represented 45.3 percent of the total sales while Japan’s Toyota, Honda Motor Co. and Nissan Motor Co. accounted for 36.5 percent.

The Toyota Corolla is the top-selling vehicle on the list, followed by the Ford Focus, Honda Civic, Toyota Prius and the Toyota Camry. There is one SUV on the list, the Ford Escape, which also comes in a hybrid model that can get up to 32 miles per gallon. Six of the top-10 selling vehicles are built by foreign manufacturers, but most are built in North America.

The prospect of extending the clunker program is causing automakers to rethink their production schedules and perhaps bring back laid-off workers.

GM’s manufacturing team was working on a production increase Thursday morning, Tom Stephens, vice chairman of product development, said in an interview.

GM has had spot shortages of compact and midsize cars, which have been popular with people trading in clunkers, Stephens said. The company also reported an increase in sales of the Chevrolet HHR small sport utility.

“Consumer confidence is really what you need here,” Stephens said. “It’s hard for them if they don’t know if they have a job or a for-sure paycheck to go out and make a major purchase, so I think this is kind of jump-starting some things.”

Hyundai Motor Co. already has added a day of production at its Montgomery, Ala., factory, while Ford Motor Co. is considering a production increase.

WASHINGTON  – The Obama administration is refusing to release government records on its “cash-for-clunkers” rebate program that would substantiate – or undercut – White House claims of the program’s success, even as the president presses the Senate for a quick vote for $2 billion to boost car sales.

Transportation Secretary Ray LaHood said Sunday the government would release electronic records about the program, and President Barack Obama has pledged greater transparency for his administration. But the Transportation Department, which has collected details about 157,000 rebate requests, won’t release sales data that dealers provided showing how much U.S. car manufacturers are benefiting from the $1 billion initially pumped into the program.

The Associated Press has sought release of the data since last week. But the public and Senate Republicans demanding more information will have to wait for details because federal officials running the program don’t have time to turn over data delivered by car dealers, said Rae Tyson, spokesman for the National Highway Traffic Safety Administration.

LaHood said in an interview Sunday he would make the electronic records available. “I can’t think of any reason why we wouldn’t do it,” he said.

DOT officials already have received electronic details from car dealers of each trade-in transaction. The agency regularly analyzes the data internally, producing helpful talking points for LaHood, White House spokesman Robert Gibbs and other officials to use when urging more funding.

LaHood, the program’s chief salesman, has pitched the rebates as good for America, good for car buyers, good for the environment, good for the economy. But it’s difficult to determine whether the administration is overselling the claim without seeing what’s being sold, what’s being traded in and where the cars are being sold.

LaHood, for example, promotes the fact that the Ford Focus so far is at the top of the list of new cars purchased under the program. But the limited information released so far shows most buyers are not picking Ford, Chrysler or General Motors vehicles, and six of the top 10 vehicles purchased are Honda, Toyota and Hyundai.

LaHood has called the popular rebates to car buyers “the lifeline that will bring back the automobile industry in America.” He and other advocates are citing program data to promote passage of another $2 billion for the incentives — claiming dealers sold cars that are 61 percent more fuel efficient than trade-ins and Ford’s Focus is the top seller.

LaHood also said this week that even if buyers aren’t choosing cars made by U.S. automobile manufacturers, many of the Honda, Toyota and Hyundai cars sold were made in those companies’ American plants.

But there’s no way to verify his claims without access to DOT’s data.

Senate GOP leader Mitch McConnell of Kentucky has argued against quick approval of $2 billion for the program because little is known about the first round of $3,500 and $4,500 rebates.

“We don’t have the results of the first $1 billion,” McConnell spokesman Don Stewart said. “You don’t have them. We don’t have them. DOT doesn’t have all of it. We’d hate to make a mistake on something like that.”

WASHINGTON  – President Barack Obama’s chief spokesman says the popular cash for clunkers rebate program may not survive beyond Friday if the Senate doesn’t provide a $2 billion cash infusion.

The program ran out of money last week. The House voted to provide another $2 billion before leaving for summer break last Friday. But the Senate must also vote before its August vacation starts Friday.

White House spokesman Robert Gibbs says the rebate program is up and running. He says anyone who wants to trade in a less fuel-efficient vehicle for a higher-mileage one should do so.

But if the Senate fails to act by Friday, Gibbs says it’s unlikely the program will be available next weekend and beyond.