On the basis of sticker price alone, used cars today are a better buy than they've been since 1981. Their prices have risen, but at a slower pace than the cost of new automobiles. Relatively speaking, it's getting cheaper to put yourself behind the wheel of a vehicle that was previously owned.

Buyers paid an average of $5,150 last year for used cars sold by new-car dealers, which are usually the vehicles in the very best condition. Average prices on used-car lots would be lower. By contrast, the average new car last year went for $11,883.

But sticker prices are only the start of the story. Discount financing has sharply cut the monthly payments on new American cars -- and you usually can't get much of a discount on a used-car loan. So in terms of cost, the new-car vs. used-car choice is not as clear as it might seem.

For example, say you're considering a lower-priced new car at around $9,000, with 10 percent down and 8.9 percent financing over four years. Your cost: about $201 a month. By contrast, a $6,000 used car, also at 10 percent down, might cost 13 percent, for a payment of $145 a month. In this example, it costs only $56 extra a month to buy new instead of used, so a new car is the better choice.

The higher the price of the used car, the better a new car looks if it carries a special financing deal.

Devotees of Japanese cars -- recently slammed with price increases of 8 to 17 percent -- might start looking at used Toyotas and Hondas. No foreign manufacturer yet offers discount loans across a broad line of new cars, but you might spot 8 to 9 percent financing through certain dealerships. If so, the cheaper loan might again give the edge to the brand-new car, despite its higher price tag.

This arithmetic hardly has been lost on used-car dealers. Traditionally, they meet competition simply by cutting the price. But today, some dealers are scratching around for cut-rate financing as a sales tool for attracting customers.

They do it by developing special arrangements with banks, which provide the dealers with cut-rate loans or, alternatively, longer-term loans than usually are offered on used cars. (You get these loans only through the dealer, not directly from the bank.) In other cases, the dealer might cut his financing charge rather than lower his price.

Dealer Frank McClure of Holmes Tuttle Ford in Tucson, Ariz., is giving 8.8 percent, three-year loans on some of the cars that have been on his lot for a while. "We decided on it as a way of stimulating business," he told my associate, Virginia Wilson, adding that he expects the offer to last for only a short time.

The vast majority of used-car buyers can't even consider new cars, McClure says, because even with discount financing, they're too expensive. But if you have a choice, you should hone in on the exact monthly payment to discover whether a brand-new car is really worth its extra cost.

A new-car dealer with 5.9 to 9.9 percent financing might reduce the value of your trade-in vehicle or insist that you pay the full sticker price -- all of which makes the car cost more than you expected. So what you gain on the financing you lose in other ways.

Also, the lowest-rate loans last only for 30 months. You'll pay much less interest than if you had taken a 48- or 60-month loan. But monthly payments will be higher, perhaps more than you can easily afford.

Although spring and summer are popular times of year for buying used cars, auction records show that's also the time prices are highest. Last year's price peak fell in June; the year before, it was July.

If you save your money and buy a used car in December -- the cheapest month on dealer lots -- you'll typically pay about 13 percent less. That saving alone could tip the scale on the side of a good used car rather than buying new.