The government's "cash for clunkers" program, officially called the Car Allowance Rebate System, or CARS for short, is in full swing, but only some consumers will be able to participate thanks to the eligibility requirements for potential buyers, their current vehicles and the vehicles they plan to buy or lease.

The program was designed to help consumers buy or lease a more environmentally friendly car, pickup or SUV when they trade in a less fuel-efficient one. Consumers can get a $3,500 or $4,500 credit toward the purchase of a new vehicle depending on the fuel economy improvement between the two vehicles, according to the government's Web site cars.gov. This credit is considered the buyer's trade-in value, and their clunker is sent off to be crushed. Here's the lowdown on the process.

Step 1: Determine if you qualify.
The person trading in the clunker must have been the vehicle's owner on the registration and the title for at least one year prior to the date of purchase, according to the program's requirements. The title must be "clear," so if there is a lien holder, you must first clear the lien before participating in the program. Consumers can only participate in the program once.

For a vehicle that has two names on one title, such as a married couple, only one person can take advantage of the program. If there are two cars with two names on each title, each person can receive a credit for each clunkers. ??

Step 2: Determine if your vehicle qualifies.
Vehicles that are traded must be no more than 25 years old and must get no more than 18 miles per gallon as a combined average fuel economy under the EPA's new estimated mile-per-gallon calculations. There are different requirements for a cargo van or very large pickup, referred to as a work truck in the program. To find the combined mile-per-gallon rating for your car, pickup or SUV, go to the EPA's FuelEconomy.gov site and select the model year, make, model and engine of your vehicle, and make sure the red number above the word "combined" is 18 or less.

Step 3: Determine if the new vehicle you want to purchase or lease qualifies.
The CARS program only applies to new, not used, vehicles that are being purchased or leased for a five-year term or longer, and have a manufacturer's suggested retail price of $45,000 or less, the program's requirements state.

If the new vehicle is a passenger car, it must get at least 22 miles per gallon in combined average fuel economy, while Category 1 trucks -- light-duty pickups, some SUVs and minivans -- must have a combined fuel economy rating of at least 18 miles per gallon. Category 2 trucks -- large light-duty pickups and some vans -- must get at least 15 miles per gallon combined, according to EPA estimates. The combined fuel economy ratings for all new vehicles ares listed on the vehicle's window sticker or can be calculated at FuelEconomy.gov. Be sure you know the make, model, engine and transmission of the new vehicle to obtain the correct mile-per-gallon number.

Step 4: Decide if it makes financial sense to participate in the program.
Consumers will receive $3,500 toward the purchase or lease of a new vehicle if it gets at least four, but less than 10, miles per gallon more than the old vehicle. They will get $4,500 if the new vehicle gets a least 10 miles per gallon higher than the old vehicle. The manufacturers have excellent calculators on their Web sites to determine how much credit you can receive for your car. Once you know how much credit you'll receive, calculate the value of your??clunker using one of the many popular auto information Web sites such as Edmunds.com, Kelley Blue Book or NADAguides.com.

If your vehicle is worth more than the amount of the credit, you may want to try to sell it yourself or trade it conventionally, without using the CARS program.

Remember, these credits are in addition to any rebates and incentives the manufacturer is offering, so this can amount to a five-digit savings or more off the new vehicle when you combine the credit with the manufacturer's rebates.

Step 5: Decide on a dealer.
At the time of publication, about 16,000 of the 20,000 franchised new car dealers were registered to participate in the CARS program, but the National Highway Traffic Safety Administration, the government agency that is administering the program, says that consumers should use its searchable database to locate a dealer to ensure the dealer they choose is participating.

Consumers do not need to register for the program. To participate, they simply reach an agreement to buy or lease a new qualifying vehicle with any participating dealer and then tell the dealer they want to trade-in their old vehicle under the CARS program. Any third party who reaches out to a consumer to try to "match" them with a dealer for the program may be committing fraud, and consumers should be cautious, the NHTSA and attorneys general in Ohio and Illinois warn.

With the majority of dealers participating in the program, you have plenty of choices as to where to take your business. Some dealers may be more willing to negotiate the price of the new vehicle than others, so choose carefully. Keep in mind that you may get a better deal if you negotiate the new vehicle price first, and then mention your interest in using the CARS program to get rid of your old vehicle.

Step 6: Complete the transaction paperwork and drive home.
Consumers should make sure that the transaction paperwork clearly outlines the terms of the sale, the applicable credits (including the $3,500 or $4,500 CARS credit and any manufacturer's rebates) and the applicable fees to ensure they are being charged appropriately. The CARS credit is deducted from the purchase price of the vehicle at the time of the sale or lease commencement. The dealer gets reimbursed via the program after it sends the old vehicle to be crushed.

The CARS program will end on Nov. 1, 2009 or when the $1 billion allocation runs out, whichever comes first. Updates on the program as well as more details can be found at cars.gov or by calling (866) CAR-7891.

Copyright 2009, Bankrate Inc.

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