Auctioneer Russ McClain of the General Services Administration says your chances of getting a used-car bargain at a federal surplus sale are better if you:

* Do your homework, which means looking at a car-price book ahead of time and checking prices at a used-car dealer.

* Determine what optional equipment the car is carrying, such as airconditioning and automatic transmission.

* Check wear on the tires (for alignment), upholstery and floormats and look for chips or cracks in the windshield. It helps you judge whether the vehicle has been "used or abused."

* Start the motor. (Regulations prohibit you from test-driving.)

Al Jacobs, who runs a car-buying service, suggests that you:

* Check for overspray of paint (on rubber trim, for example) or file marks that may indicate the car needed bodywork after a collision.

* Look for rust, especially in the wheel wells.

* Look at wear on the brake pedal, to help judge if the mileage figure is correct.

* On cars with automatic transmissions, pull the transmission stick while the engine is running. "The fluid should be pink. If it is black or has a charcoal smell, you may have transmission problems. It could cost you $400 to $500 for repairs."

* Check the engine oil for cleanliness. If it is sticky, that could be a sign it contains an oil additive because of excessive oil consumption.

* Keep a fixed price in mind, and don't overbid in the heat of the moment.