When it comes to the purchase of a used car, the law is quite clear: Whatever goes wrong after you leave the lot, if you buy the car "as is," is your responsibility.

But how do you know that you are buying the car "as is"? And what do you do when you buy a used car, thinking you have implied warranty protection, and the dealer contends that you don't?

Rondah Kinchlow, a local radio newscaster, is struggling with those questions right now.

In November she bought a 1975 copper-colored Volvo with nearly 91,000 miles on its odometer from Waldorf Toyota-Volvo. The price was $2,500.

"Cosmetically, it is a beautiful car," said Kinchlow, who works at WTOP radio.

But she began having problems with the car less than a month after she got it, she said. One mechanic has told her that the car needs $1,200 worth of repairs, including a new alternator, front suspension work, front end realignment and sunroof repair.

Kinchlow took the car back to the Volvo dealer in December for repair. "They kept the car three weeks and then told me they weren't going to fix it because I had purchased the car 'as is,' " she said. ". . . I don't recall signing any documents suggesting that."

Larry Brinsfield, used car manager for Waldorf Toyota- Volvo, said yesterday that Kinchlow had been told "up front" that she was buying the car "as is" and that there was a handwritten disclosure on what he described as a "purchase order."

"There was no deception," he said.

Told that Kinchlow had been unable to find any written disclosure in her car purchase papers, Brinsfield said, "Maybe she lost the part that said that." He declined to answer further questions, saying he was "jammed up" with other business.

Kinchlow, in the meantime, has sought the assistance of local and state consumer officials in resolving the stalemate with Waldorf Toyota-Volvo.

George Rose, chief of the automobile section of the Montgomery County Office of Consumer Affairs, said there appear to be two basic issues in this case:

* Whether Waldorf Toyota-Volvo complied with the Maryland law for the "as is" sale of a used car. A used car has an implied warranty when it is less than six years old and has been driven less than 60,000 miles. When the dealer sells a used car more than six years old that has been driven more than 60,000 miles, the car still has an implied warranty "unless the buyer waives that protection by signing a special form prepared by the Motor Vehicle Administration that she is responsible for the repairs."

* If there is no evidence that Kinchlow signed such a form for the Volvo, then she technically is entitled to the implied warranty. How much that is worth depends, Rose said.

"Something like this is never easy to determine, but when you pay $2,500 for a car, that indicates it has value and that it isn't junk," he said.

Warranty protection available to Washington area consumers depends on where the used car is purchased. The District provides for an implied warranty, regardless of the car's age or mileage at the time of sale, according to Henry Lee, chief of the city's consumer complaint office. The dealer can reduce his responsibility for what goes wrong with the car later, however, by giving the customer a written list of what's wrong at the time of sale, Lee said.

In Virginia, the only warranty protection is what you get in writing, according to Mary Ann Shurtz, director of the state consumer office in Northern Virginia.