“Cash For Clunkers” starts today

The federal government will now pay $3,500 or $4,500 for your old, gas-guzzling car or truck when you trade it in for a new vehicle.

The Car Allowance Rebate System (as it’s formally called) runs through Labor Day.

If you qualify, the rebate is incredibly easy to get. The dealer does all the work and deducts the rebate from what you owe on the car or truck you’re buying.

Here are the basic rules:

• The car or truck you’re trading can’t be older than a 1984 model (although there are slightly different rules for larger trucks).
• It can’t have a combined fuel-economy rating of more than 18 miles per gallon. To see if your vehicle qualifies, go to fueleconomy.gov.
• The vehicle must be drivable, and legally owned and insured by you for at least one year.
• The sticker price of the new car or truck can’t exceed $45,000.
• The combined fuel economy estimate for the new vehicle must be at least 22 m.p.g.
• Your new car or truck must get at least 4 m.p.g. better than your old one. If the difference is between 4 m.p.g. and 9 m.p.g., then you’ll qualify for $3,500. If the difference is 10 m.p.g. or more, you’ll get a fat $4,500.

The rules are a little different if you’re trading a pickup, sport-utility vehicle or van in on a similar vehicle.

For small pickups, SUVs and minivans (which are considered “Category 1″ trucks in the CARS program), the traded vehicle’s fuel economy cap is the same as for cars, 18 m.p.g.

But if you’re buying another Category 1-type vehicle (trading a clunker minivan for a new minivan, for instance), the new vehicle only needs to get 20 m.p.g. to qualify for the program.

If it gets 2 m.p.g. to 4 m.p.g. better fuel economy than your old truck you’ll qualify for a $3,500 rebate. If the difference is 5 m.p.g. or more you’ll qualify for a $4,500 rebate.

“Category 2 trucks” are mainly full-size pickups and vans.

If you have one of these, you don’t have to worry about the 18 m.p.g. cap. They’re all eligible for the program.

But if you’re replacing an old Category 2 truck with a new Category 2 truck, the new one has to get at least 15 m.p.g. and deliver a 1 m.p.g. improvement to qualify for the $3,500 rebate and a 2 m.p.g. increase for the $4,500 rebate.

The National Highway Traffic Safety Administration is in charge of the CARS program and has created a Web site called cars.gov to answer questions.