PHILADELPHIA (MCT) — "Cash for Clunkers" won't single-handedly save the environment, rescue the beleaguered auto industry or spare consumers from financial distress.

But the new $1 billion federal program promises a little help in all three areas, a bit of political symbiosis that explains why the plan motored through Congress three weeks ago on the back of an Iraq war-funding bill.

Once it gets rolling later this month, the program will offer incentives of $3,500 or $4,500 to those who buy or lease a more energy-efficient new vehicle. The goal is to get people to trade in a qualifying gas-guzzler — car, sport utility vehicle or light truck — for a comparable vehicle that gets substantially more miles per gallon.

The program's narrow focus has drawn criticism. Still, lawmakers are hopeful that it will make a small dent in energy use and pollution, as well as jump-start depressed auto sales. Without it, automakers are on pace to sell just 10 million new vehicles in the United States this year — down dramatically from 16 million in 2007 and 13 million in 2008, according to Edmunds.com, which compiles data on the industry.

One limitation is the window of opportunity. Although the rebates theoretically became available Wednesday, they are unlikely to spur sales until final procedures are announced, probably around July 24. Until then, car dealers could be on the hook if they credit buyers with incentives and are unable to collect from the government.

At the other end, the program expires Nov. 1 — or whenever the money runs out. Given that its backers initially proposed spending $4 billion to promote the purchase of a million vehicles, and that a similar program boosted Germany's car sales 40 percent in May, the spigot could run dry before November.

Of course, Congress might relent and extend the program. And meanwhile, the funding cap may help by pushing fence-sitters to act. Auto dealers say Cash for Clunkers already has captured buyers' attention and may even be dampening sales as vehicle-shoppers await the help.

"We're having customers come in and ask about it every day, or say that they're waiting for it every day," said Ross Choate, managing partner for the John Kennedy Ford, Mazda and Subaru dealerships in Philadelphia's suburbs.

After a relatively good May and early June, Choate said, sales slowed as Cash for Clunkers drew headlines.

"I do think it's holding people up," he said.

Here are answers to some key questions about the program, formally called the Car Allowance Rebate System: