Some of the car ads for low-rate financing have a fishy smell -- and you're the sucker who is on the hook. These auto dealers are reeling you in with what looks like a bargain. But they've simply found a hidden way of getting you to pay top price.

So deceptive is this approach that state officials and business groups, including some auto-dealer groups, are taking action against it.

* In Minnesota, under steady pressure from the attorney general, a code of advertising has been adopted to prohibit illusionary low interest rates that, says the Better Business Bureau's Ron Graham, violate the state's consumer-fraud law.

* In Boston, the BBB issued a consumer alert, "because we feel this type of advertising has been deceptive," BBB President Leonard Sanders told my associate, Virginia Wilson.

* In Washington, the BBB sent out a special letter to auto dealers about a number of misleading advertising practices. Auto advertising runs in cycles -- oscillating from good to bad -- the BBB says, and "is now at a low point."

One of two new sinkers getting by consumers today is the auto "buydown."

In a buydown, the auto dealer arranges with a lender to give you a low-rate loan, maybe at 6 to 10 percent interest. To persuade the lender to make such a loan, the dealer adds a lump-sum payment in cash. He then recovers his cash payment by raising the price of the car or the price of the options that come with the car.

You may believe you're getting a bargain. but in fact you are paying extra for the car in three ways: The stated price itself is higher. The sales tax is higher, because it is figured as a percentage of the stated price. Buyers who itemize their tax deductions are getting a lower tax write-off, because of the deceptively lower interest rate.

It's often hard to know when you're involved with buydown financing. Recently, dealers were offering legitimate low interest rates (8.8 percent) on many models as an inducement to buy. These rates were subsidized by the manufacturers and did not increase the price of the car.

The problem loans are those offered strictly by a dealer, with no participation by the manufacturer. In theory, the dealer, too, could subsidize your interest rate. But in practice, he usually charges you for it in a hidden way. Low, buydown rates also may require large down payments -- unmentioned in the ads or disclosed only in tiny type. The object is to bait you with an apparent low rate, get you into the showroom and sign you up.

How can you tell when you're being snookered? Suspect any unusually low interest rate; call the auto manufacturer's zone office to see if the company is subsidizing interest rates; comparison-shop with other dealers, to find out what the car you want really should cost; look for telltale fine print in the ad, saying something like "dealer participation may affect the price you pay."

You've definitely been had if the dealer claims that he has sold all his models that carried low-interest-rate financing, but can show you something nice at a higher interest rate.

Another sinker is auto leasing. Some dealers make their leases look much cheaper than buying the car outright, which, for the average buyer (who can't deduct lease payments as a business expense), is rarely true. The Dallas BBB is troubled by ads touting low monthly payments without disclosing that the payments are on a lease.

When you lease, you merely are renting the car for a certain period. The monthly cash payments may appear to be lower, but you get no tax deductions (as you would for finance charges on a purchase) and you lose the trade-in value. You will have to buy the car at its used-car price if you want to hang on to it when the lease expires.

A few things to watch for in leases: You may pay an extra 6 to 10 cents a mile if you drive over 15,000 miles or so. With an open-end lease, you may pay extra if the car depreciates faster than expected. (Closed-end leases cost more, but you run no price risk when the lease expires.) There may be built-in balloon payments at the end of a lease. You may not get all of your up-front deposit back.

The advantage to a lease is that you pay only a small amount up front, which for some drivers is all that matters. But you're getting convenience rather than a bargain.