t's time. Either your present car is old and unreliable or you want something safer and more economical. Or maybe you just want a change. Whatever the reason, though, you still must decide: Should you buy a new car or a used model?

Who doesn't want a new car? Shiny paint, up-to-the-minute styling and cutting-edge technology, the promise of smooth, quiet, trouble-free operation, that "new car smell" - all of these things whet the appetite for ownership.

There's more, too, even from a practical side. "When you buy a new car one of the things you get is the peace of mind of a decent warranty," Jack Gillis, consumer advocate, author of The Car Book and Director of Public Affairs for the Consumer Federation of America, told CarPoint. "There's also the psychological aspect of having something that's yours that you have the opportunity to maintain from the get-go," he added.

Owning a car from its beginning is important if you are the kind of person who prefers to hang on to a vehicle for more than the usual number of years. (Most car owners keep their vehicles four to six years, according to the National Automobile Dealers Association, the industry's leading trade organization; but more than 20 percent of owners keep their vehicles nine years or longer, reports a 1996 survey by J.D. Power and Associates, automotive market researchers.) By owning a car or truck from the outset, you can make sure it receives the care needed to reach the limits of its intended life span; and you also will know the entire history of the vehicle, and so will not likely encounter any surprises.

Of course, buying new also "gives you more control over choices," said Gillis, meaning that whereas used car buyers are limited to what is available on any given lot, new-car buyers can get dealers to obtain different models from other dealers, and can even have cars built to order by the manufacturer.

Charles Vogelheim, editor of Kelley Blue Book vehicle price guides, pointed out to CarPoint that buying new is practically the only way to obtain a car or truck that is both innovative and popular. With an in-demand vehicle, said Vogelheim, "it will be a long time before any used models hit the market, and with people waiting in line for them the price won't come down much."

Indeed, price is the primary reason most people consider buying used cars. In a 1996 study by the Dohring Company, a market research firm, 72 percent of survey respondents said that the price of new vehicles was the reason they would consider purchasing a used vehicle, and less than half (49 percent) said they'd rather purchase a $15,000 new vehicle than a used higher-end vehicle whose price had dropped to $15,000 from its original new-car figure.

"Used cars provide the opportunity for someone to purchase a car of their choice for less money, or to step up to a better model," said Vogelheim. The reason is simple: the original owner has already absorbed the largest depreciation hit, so you don't have to. Jack Gillis agreed: "Our findings are that a used car can cost 50 percent less overall to run compared to a new car."

From the moment you drive away from the dealership you car loses value. The largest drop, often as much as 20 percent of the purchase price, occurs during the first year. After that, the decline is less steep. Depreciation accumulates as "a percentage of a percentage of a percentage, each year," explained Vogelheim; so typically the amount changes by smaller and smaller increments as the car ages. However, the rate of depreciation is not uniform, because of ungovernable changes in the automobile marketplace. As a result, some cars hold their value better than others, but often for different reasons.

These days, a car bought several years into its life span has stabilized greatly in value but has neither declined significantly in mechanical reliability or appearance nor increased in ownership costs. (In fact, insurance costs and other fees often are considerably less than when the car was new.) Therefore, if your main goal as a vehicle buyer is obtaining reliable transportation for a good price, the used-car market can be the best place to shop.

The most promising areas are the emerging segments of "near-new" and "certified used" cars. Near-new cars generally are two to four years old and began life as vehicles sold to lease customers. Because of the stringent mileage restrictions and maintenance requirements that are part of most leases, these vehicles practically qualify as new, even in appearance; and they usually are still covered by their original warranties.

Certified used cars are vehicles that have been refurbished to like-new standards and have passed a checklist of requirements that are the basis for certification. It is important to know whether a used vehicle is dealer-certified or manufacturer-certified, since the standards for each may differ. Nevertheless, certified used cars provide the same peace of mind that traditionally comes only with buying a new car.

Deciding whether to buy a new or used car should start with asking yourself what your strongest interests are in owning a vehicle. After that, compare prices and financing opportunities. If you decide to buy used, choose a certified used car - "either a near-new" or an older model. "Whatever you do," warned Charles Vogelheim, "buy from a dealer unless you know the seller well, so you'll have a place to go back to if something goes wrong with the car."