Senator Eliot Shapleigh - El Paso, Texas

Cars traded in the cash-for-clunkers program go to junkyards like Hackensack Auto Wrecker and Repairs in New Jersey.

WASHINGTON — As problems go in the nation’s capital these days, the White House could live with this one.

By late Thursday afternoon, they ran to the White House with news that they might have committed the whole $1 billion, or even more. This stimulus program had, in fact, stimulated very heavy demand, which required a quick decision about what to do next.

Over the course of 24 hours, the White House changed its mind three times. At first, it said it would shut off the incentives by day’s end. Then it let them continue through Friday, and then through Sunday.

On Friday, the House voted to add $2 billion, soothing the fears of car dealers, who would have been responsible for paying any money they promised to customers as a rebate. But the Senate might not follow suit. Some senators said Friday that the speed at which the money flew out the door was a sign that the government’s deal was too good, and perhaps should be modified.

But still, a question remains: What was behind the apparent last-minute run on the clunker fund?

The answer appears to be a bad mix of paperwork and balky computers.

Around the country, dealers had put off the laborious task of applying for the rebates of $3,500 or $4,500, which requires entering the 17-character identification numbers of each vehicle to be scrapped, scanning images of proof of insurance and filling out other paperwork.

The computer system was overloaded, according to the dealers. They said they would finish one page in the application, hit enter and nothing would happen. Eventually a message would appear notifying the dealer that the page had “timed out.”

Tom Frew, the business manager at Galpin Motors in Los Angeles, said that he needed 35 tries to register just one of the company’s 11 dealerships on the day that the program opened because of problems with the government Web site. On Friday, he spent an hour processing just one rebate application, he said.

“It’s probably anywhere from 30- to 60-second delays between mouse clicks,” he said. Each application can have up to 11 attachments.

But sitting in front of a computer is not the top priority for most of the company’s employees — instead, their job is to “aggressively go out and handle all the customers that are flocking to the showrooms,” he said.

The National Automobile Dealers Association told Transportation Department officials on Thursday that its members had submitted about 22,000 applications, but were sitting on tens of thousands more, said Bailey Wood, a spokesman.

“Dealers are interested in one thing, moving metal off their lots, not sitting at the computer and doing data entry,” he said.

A Transportation Department official said the agency had already run two instruction classes over the Internet on filling out applications, and was planning a third. A computer contractor, Oracle, has enhanced the capacity of the government Web site.

Cash for clunkers is an unusual government program, because dealers sell the cars, then wait for repayment from Washington. Government officials do not want to commit to more than Congress has appropriated because, under the Anti-Deficiency Act, they can be fired, fined and even jailed for doing that.

Dealers say failure to be reimbursed would be a nightmare for them. At Galpin Motors, Beau Boeckmann, vice president, said his company would try to “unwind” the sale, get the slightly used car back and try to sell it again.

Amid the confusion of Thursday afternoon, when the Transportation Department said the program would end that night, Galpin’s sales staff called anybody who had stopped by their dealerships recently and quickly sold 30 Fords and 20 Hondas.

Mr. Boeckmann said he was relieved that the program would run at least through the weekend; his company was already locked into print and broadcast ads featuring the rebates.

Despite the malfunctions, the House voted 316 to 109 to shift $2 billion from the Energy Department’s loan fund into the clunker program. Democrats were joined by all the Republicans in the Michigan Congressional delegation, and half of those in Ohio.

The Senate will take up the matter next week. A spirited debate is likely, as some senators have said they will use the opportunity to push for tougher fuel-efficiency requirements. If the Senate does not go along with the House’s version, the House might have to return to work on a compromise.

Mrs. Feinstein and Senator Susan M. Collins of Maine, a Republican, said in a statement, “We will insist that any extension of the program requires that the minimum fuel economy improvement for newly purchased vehicles be at least two miles per gallon higher than it is under the enacted clunkers program.”

Senator Charles E. Schumer of New York also said that the Senate should be open to making the mileage rule stricter. Many environmentalists said the government was getting too little improvement from taxpayer dollars.

President Obama, though, seemed to favor a straightforward extension. “We’re already seeing a dramatic increase in showroom traffic,” he said after the House vote, adding that the program helps to reduce air pollution while helping car buyers.

Robert Gibbs, the chief White House spokesman, offered assurances that the administration was looking for ways to continue the popular new program.

“If you were planning on going to buy a car this weekend using this program, the program continues to run,” he said. “If you meet the requirements of the program, the certificates will be honored.”

Mr. Gibbs declined to say how long the program could continue without an infusion of money.

But Representative Steve Israel, Democrat of New York, an early advocate of cash for clunkers, said, whatever happened, more would have to be done in September. “We estimated a billion a year,” he said. “It’s about a billion a month.”