It was bound to happen: The auto leasing boom has begun to spill over on to used-car lots. With about 2 million two- and three-year-old vehicles coming off lease this year, some auto makers are cranking up leasing programs to help unload them. To make the cars more alluring, they're offering extended warranties and roadside assistance. Some have even started subsidizing leases to lighten monthly payments.

Of course, buying is still the cheapest option over the long haul. Leasing a 1992 Lexus LS400 for three years, then purchasing it over the next two, costs roughly $700 more than simply taking out a five-year loan. Most people, meanwhile, don't even purchase the leased car, and they end up owning nothing. So if you drive cars until they fall apart, you're better off buying. Likewise, if you drive more than average, steer clear: Most leases charge premiums of 10 cents or 15 cents for every mile over 15,000 a year.

LEMON RELIEF. Still, leasing may have big appeal for some. It lets you drive a fancier car, since the payments are usually lower. It's also attractive to those who can't pony up the typical 10% used-car downpayment--or who would rather spend the money elsewhere. That's even truer now that some carmakers are refurbishing used cars and offering extended warranties that mimic those of new models. Such steps remove some of the risk of mechanical problems. Best of all, if the car turns into a repair headache, you can walk away at the end of the lease.

So far, pricey brands such as Jaguar and Lexus have pushed hardest into used-car leasing, but more prosaic marques such as Ford are test-marketing programs to help move the metal, too. As the number of used cars coming off lease continues to grow, expect a spate of attractive promotions.

Tread carefully, though. For starters, leasing a used car or truck can be nearly as expensive as choosing a new one. A typical 1992 Mercedes 300E goes for about $600 a month on a four-year lease--the same price as leasing a new 1995 E320. That's because Mercedes figures the '92 will depreciate by about the same dollar amount over four years as the new version. Obviously, in such

instances, you may as well drive the new one. Leases for late-model luxury cars often are close to new-car deals, so often your best bet is cars at least four years old.

That said, there are still good deals to be had. In particular, luxury-car makers, who must unload a flood of cars coming off their first lease this year, are worth checking out. You can lease a 1992 Lexus LS400 for three years for $600 a month, vs. $850 a month for the new, redesigned '95. Be sure the car is a "certified pre-owned" Lexus. That designates a car that has been refurbished, has passed a rigorous inspection, and is backed by a factory warranty for an additional two years, or up to six years and 70,000 miles. And you can receive service at any Lexus dealer.

Carmakers have various names for their programs. At Mercedes, it's called Encore Lease, and at Jaguar, Select Edition. Sometimes such tags designate a special deal. Mercedes offers interest rates as much as 2.5 points lower on Encore leases than on others. A 48-month Encore lease for a 1990 300SEL runs about $545 a month with no downpayment, $50 less than a non-Encore lease, says Garth Blumenthal, general manager of Fletcher Jones Motorcars in Newport Beach, Calif.

AEROSTAR WARS. For now, good lease deals are tougher to find on more mainstream wheels. Watch the ads. You could get lucky if supplies of a vehicle balloon. Last year, Ford tested a used-car leasing program with rates as much as three points below the 8% average. The result: Folks could lease a two-year-old Aerostar minivan for $260 a month over two years, vs. $325 a month to buy one over four. Leasing some Japanese models, such as a Toyota Camry, can make sense because their low depreciation rates help cut payments.

Before you sign on the dotted line, check behind the monthly payment to be sure you're getting a fair shake. Compare the car's price, or "capitalized cost" in lease-speak, with an independent source such as the National Automobile Dealers Assn.'s Official Used Car Guide, available at banks and many libraries. Then, find out the "residual value," or the estimated value of the car at the end of the lease you're being offered and compare that with the Automotive Lease Guide (813 791-4955, $12.50 an issue). If the salesperson refuses to give you that info, you're probably being overcharged. If the math adds up, though, slide behind the wheel and take your used dreamboat for a shakedown cruise.

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