``Beauty,`` it has been said, ``is only skin deep, but ugly goes all the way through to the bone.``

Such is the case with Honda`s newly designed Civic Si hatchback, the runt of the Japanese automaker`s litter.

The Civic hatchback is offered in CX, DX, VX and sporty performance- oriented Si version, the one we test-drove.

The function of the Si is to rack up mountains of miles without having to stop for fuel. The rating is 29 m.p.g. city/36 m.p.g. highway with the 1.6- liter, 16-valve, 125-h.p. four-cylinder engine teamed only with a five- speed manual.

Even though you can pass most gas stations without having to stop, the price you pay is having to cover the machine with a tarp once you reach your driveway-to protect you from the giggles or outright guffaws of friends and neighbors who see it.

With the Civic Si`s light weight (2,326 pounds) and small subcompact dimensions, it`s obvious why the mileage is so high. We`d swear the car ran on fumes without having to dip into the gas supply. The needle hardly budged.

While fuel economy is a big plus, the performance from the sports- oriented Si we test-drove was a bit disappointing. It sure didn`t feel as if 125 horses were pulling only 2,326 pounds.

For 1992, the front-wheel-drive Civic has undergone a design change to the rounded aero look. It also has grown a bit in size. Wheelbase was extended to 101.3 inches from 98.4 inches and length grew to 160.2 inches from 157.1 inches. There`s ample room up front to stretch legs and arms. In back, those legs and arms better be attached to preteens if you want to get the person out again.

The hatchback`s elongated rear-end design makes the car look like a mini station wagon. Adding to the dumb styling is a rear spoiler extending out over the hatch glass in back that looks like an awning.

The new design for `92 tapers the glass on the rear side window. The effect is to make the glass look ``pinched,`` and thus smaller, which only magnifies the awning look from the spoiler.

The rear hatch has separate glass that swings up and a tailgate that swings down. The gate is very small and rounded and, as a ledge, leaves the ability to balance a sack of groceries to be desired. The rear seats fold flat so you can haul more cargo, but the tailgate provides some interference in loading the vehicle from the rear.

Standard equipment includes power brakes and power steering, power sunroof, 14-inch tires, front stabilizer bar, dual power mirrors, cruise control, quartz digital clock, intermittent wipers, rear-window wiper/washer/ defroster, coin box, passenger-side vanity miror, split/individually foldling rear seats, tinted glass, pop-out dual cupholders and adjustable steering column.

The Civic offers a driver-side air bag as standard, but no anti-lock brakes.

Base price is $11,900. Add $720 for air conditioning and $474 for AM/FM ster eo.

The Si`s mileage is great, but if you want a car that looks like a wagon, you might as well wait until this fall when the Saturn station wagon bows, complete with a driver-side air bag and ABS-plus plastic body panels that won`t rust. More important, the prototype that made the rounds of the auto shows this year is considerably more pleasing to look at than the Civic Si hatchback.