Okay, so you've decided to make a personal statement and lay out $25,000 or so for that mean driving machine you've been admiring in the ads and on the dealer's lot. You can't wait to see the envious expressions on the neighbors' faces as you wheel up in a gleaming hunk of glass and chrome that cost you what the median American family earns in a year.

Unfortunately, your dream machine may have other admirers. The Dead End kids from across the tracks might be just dying to take it for a midnight spin. Worse yet, the local representative of some East Coast chop shop may find it perfect grist for his employer's mill.

Auto theft is a growth industry. More than a million vehicles are stolen each year, according to FBI and insurance industry data, and in 1986, the most recent year for which complete figures are available, an additional 1.5 million cars suffered thefts of contents and 1.2 million more had accessories swiped.

At that rate, according to the National Automobile Theft Bureau, one out of every 46.2 registered motor vehicles was either stolen outright or had something stolen from it.

The nation's tab for auto theft, including law-enforcement costs, exceeded $6 billion in '86, the NATB figures.

Locally, Maryland recorded 24,334 thefts of vehicles in 1986, up 20.2 percent from the year before; the District showed 6,105, up 21.5 percent, and Virginia had 12,702, up 13.2 percent. The Washington metropolitan area itself recorded 20,415 vehicle thefts in 1986.

If you find that alarming, you should. But within the insurance and auto industries the response has been largely one of confusion.

Consumers looking for protection -- and companies leaping to try to provide it -- have spawned a multibillion-dollar industry of burglar alarms, add-on locks and "disabling devices."

These gadgets range from highly effective to utterly useless. Prices range from a few dollars to more than $1,000 (and the price doesn't always correlate with effectiveness), any of them can be defeated by an experienced and determined thief, and some of the best ones are factory-installed and only available on a few models.

The multiplicity of gadgets seems to have in turn stymied the insurance industry. Since insurance bears the brunt of the economic loss, it would seem logical that insurers would be pushing the devices and giving rate breaks to motorists to have them.

Indeed, the Insurance Services Office, a company that advises small insurers on rates, actuarial risks and the like, recommends that insurers offer discounts of from 5 to 15 percent on the comprehensive portion of their auto policies to motorists who have the devices.

So far, however, few companies are doing so. Of the four largest companies operating in the District, Maryland and Virginia, none gives such discounts, though Geico is considering it.

Typical is Allstate's view. According to spokesman Jack Turbidy, "Our experience as a company has been that there are so many devices -- some work extremely well, some don't work at all, and it's difficult to tell which work and which don't." Consequently, across-the-board discounts would cut rates for bad devices as well as good ones.

In a half-dozen states, legislators or regulators have stepped in to mandate the discounts, which range up to 20 percent on the comprehensive portion of the policy, but most commonly are in the 5-to-15-percent range, depending on the type of device.

The states, though, are relying on general guidelines, rather than rating the individual devices.

So what's a consumer to do?

First, decide if you need such an antitheft device at all. If you have an expensive car and live in a metropolitan area -- or regularly park in one -- you should consider one, insurance industry officials say. Likewise if you own any type of sports car.

Noted Daniel W. Kummer of the Alliance of American Insurers: "Whether you get a {insurance} credit or not, the device serves a useful purpose." Second, you can look to the various state rules -- and your own driving habits -- for general guidance.

The top-rated systems are called "passive disabling devices." Passive means that the driver doesn't need to do anything to arm them. Disabling means that they prevent the car from being driven, usually by shutting off the fuel or ignition or both. Insurers and regulators prefer these to "active" systems because there is no worry that the driver will rush off and forget to set them.

But the passive systems are the most expensive, and usually require professional installation. So if you are very conscientious, something you have to set can be just as effective. Some of these are very simple gadgets that lock the steering wheel and/or brake or gas pedal.

"Anything that can slow down a thief" is a help, said Harvey Seymour of the Insurance Information Institute. " ... The more problems you throw in the way of a car thief, the more likely he is to say this is too much work, and look for an easier target across the street."

MORE ON D.C. BONDS ... A passing reference in this column last week to the impending end to the District's blanket tax exemption for municipal bonds from other jurisdictions apparently caught a number of readers by surprise, and many called seeking additional information. The situation, in brief, is this:

In the pre-Home Rule years, the District did not issue municipal bonds of its own, but instead met its capital needs by borrowing from the U.S. Treasury. But in 1982, to bring its tax code into conformity with federal law and in anticipation of entering the bond market, the City Council voted to begin taxing bonds from other jurisdictions.

To ease the impact on D.C. residents, the council provided a 10-year grace period for individual (though not corporate) taxpayers, and included a grandfather clause: Tax-exempt bonds bought by a city resident on or before Dec. 31, 1991, will continue to be tax exempt. Such bonds -- other than ones issued by the District -- that are bought on or after Jan. 1, 1992, will be taxed.