THE 1991 GEO Metro LSi Convertible is a topless illusion, a neat little golf cart posing as a car. That is not to say that it's some awful thing. It's cute. It's peppy. It runs forever on a tank of 87-octane unleaded gasoline. Used within its limits, it's a delightful set of wheels.

But it's the limits that bother me -- like the limits of what the Metro Convertible can take in a crash.

This car is tiny, folks. It weighs 1,753 pounds, in league with some big motorcycles. Its wheelbase, the centerline distance between the front and rear wheels, is 89.2 inches. Its doors close with a "tink" instead of a "thonk." It gets blown about on expressways.

This nymph of a two-seat, front-wheel-drive convertible does have an air bag on the driver's side. That's good -- for the driver. What happens to the passenger in a car this light and small, especially if the passenger is unbelted in a crash, is something I do not wish to contemplate. Also troublesome to ponder is the fate of occupants in this motorized matchbox if they take a good hit in the side or rear.

I do not wish to be alarmist, nor to cast doubt unfairly upon what is otherwise a very decent automobile. But the Department of Transportation, in an exhaustive study published this year, has raised serious questions about the safety of small cars -- no matter how well they are built, no matter who makes them.

It has something to do with the laws of physics, which are far less compromising than the laws of man. If you buy this one, drive it carefully -- very carefully.

Background: The Geo Metro LSi Convertible is one of seven mini-vehicles supplied to General Motors Corp. by its Japanese partners -- Suzuki, Isuzu and Toyota. The Metro comes from Suzuki.

There are six versions of the Metro car, the least expensive of which, the XFi hatchback, gets 55 miles per gallon. The two-door convertible is the top of the line. All Metro cars are base-priced under $10,000.

Complaints: The eerie lightness of being. You feel the wind in this little car, regardless of whether the top's up or down. On the highway, you feel like an ant on micro-skates. You get used to all of this tiny business eventually. It simply takes a nerve adjustment.

Praise: Fuel efficiency. The Metro Convertible gets an astounding 46 miles per gallon, when equipped with the standard five-speed manual gearbox. With its 10.6-gallon tank, the car can run for an estimated 482 miles on its usable volume of fuel (the part that doesn't evaporate or is lost in idling).

Another thing: Though a scamp of a car, the Metro Convertible has an okay trunk, 6.4 cubic feet, enough to bring home groceries.

Head-turning quotient: The car's definitely cute. It attracted attention wherever it went.

Sound system: AM/FM stereo radio and cassette by GM/Delco. Very good.

Ride, acceleration and handling: Good ride on good roads. Bad ride on bad roads. You will feel the bumps. Avoid potholes at all costs.

Acceleration is peppy, but not durable. The little Metro Convertible begins to whine mightily at sustained highway speeds. If it could talk, it would say: "Geez, c'mon. I'm tired of this. I wanna slow down and go home."

No wonder. The car is equipped with a one-liter, three-cylinder, 55-horsepower engine -- great for short commutes, lousy for long runs.

Price: Base price on the Geo Metro LSi Convertible is $9,740. Dealer's invoice price is $8,961. Price as tested is $10,665, including $670 for the air conditioner and a $255 destination charge.

Purse-strings note: Life is a matter of trade-offs, and you're making certain trade-offs in buying the Metro Convertible or any other similarly sized car. You're trading some significant safety margins for fuel economy and the topless look. It's as point-blank as that.

Warren Brown covers the automotive industry for The Washington Post.