The Buick Skylark test car was a study in deception. At first glance, and perhaps even at glance two or three, it looked like a nice steady mom-and-pop four-door sedan. The gray exterior and interior didn't add to its image. Absolutely nothing wrong with this type of car, there are plenty around, but it could hardly be called exciting.

If someone bothered to look at the tires, though, the game might be afoot. What are raised white letter performance tires doing on an innocuous-looking sedan? Well, the test car was not as innocent as it appeared. For starters it was a top-of-the-line Limited model. And it was equipped with the Gran Touring Package (for handling) and the new Quad 4 double overhead cam engine (for power). It just gets more curious.

The Skylark, as with many other cars, can have a variety of personalities, each depending on what the buyer wants. The test car (supplied by Kelly Buick, State Street, Emmaus), obviously, was one of the more interesting personalities and would appeal to those who enjoy the performance that goes with a sports sedan; though I am sure these qualities would not be wasted on what is known (though not defined) as the average driver.

Buick and Skylark go back a number of years. In fact, Buick, one of the oldest car companies in United States and, for that matter, the world, is celebrating its 85th anniversary. The Skylark is not quite that old but it has been around. The Skylark is generally thought of as a smaller Buick. The name, though, was introduced on a limited-production, full-sized convertible in 1953 as a sort of a tribute to the company's 50th anniversary. However, it was first used for a small car (or what went for a small car in those days) in 1961, and with the exception of the 1973-74 model-year when Buick tried to cash in on the space program and changed the name to Apollo, this popular name has been in the lineup ever since.

Anyway, even with itssports sedan suspension system and more powerful engine, the test car was not the least bit difficult to drive. A little livelier, perhaps, but not really demanding. Its smaller size (smaller than several other Buick models), of course, makes judging, maneuvering and parking a little easier.

With a wheelbase of 103.4 inches, overall length, 180.1 inches; width, 66.1 inches; height, 52.1 inches, and curb weight of 2,638 pounds, the car is, indeed, compact sized. Its EPA volume rating of 104.4 cubic feet falls almost smack center in the middle of this classification - that is, cars measuring 100 to 110 cubic feet in volume.

Buick calls the Skylark sedan its ''little limousine'' and who can argue? The car, especially in its Limited trim, does have an ambiance usually associated with a larger car. However, no matter what you call it or how you cut it, it still is a compact and only provides as much interior room as other compacts. Front seat room is good and b ack seat leg room for adults could be a little tight if the front seats are extended fully aft. Trunk room, at 13.4 cubic feet, is decent though not outstanding.

The test car's interior gave a more sporty appearance with a full-length console housing the automatic transmission shift selector and parking brake. The optional electronic instrument panel wasn't as bad as most. The cluster includes speedometer, odometer, fuel lever gauge with expandable reading for the last one-quarter tank and a multi-functional gauge. The last item is the most interesting. It combines a tachometer and volts, temperature, oil pressure gauges in one unit and choice is made by pressing a selector button. Maybe a little spacey but not bad.

The standard engine in the Skylark is a 2.5-liter/151-cubic-inch overhead valve four-cylinder. This engine produces 98 horsepower and should provide adequate horsepower for all Lehigh Valley driving conditions. There is also an optional 3-lit r/181-cubic-inch V-6 rated at 125 horsepower that will certainly put a little zing in your driving.

As mentioned, thought, the test car had the new Quad 4, the first (modern) double overhead camshaft, four valves per cylinder engine offered in a mass produced American car. (The engine also is used in other General Motors division cars.) This type of engine is not really new (what else is?) but it has had a revival in the past couple of years because it can get fairly high horsepower out of small displacement engines (without reverting to turbocharging) and is ''clean'' and can easily meet emission standards. In fact, the Quad 4 is so clean it doesn't need an exhaust gas recirculation system to meet 1988 emission requirements. Buick also claims it is engineered to be reliable, durable and have a long service life. Well, time will tell on this one.

The multi-port fuel-injected Quad measures 2.3-liter/140-cubic-inches and is rated 150 horsepower at 5,200 rpm and 160 foot pounds torque at 4,000 rpm. As one can see, this is quite a bit of horses for its size. Enough horses to move the Skylark from 0 to 60 mph in about nine seconds. And this is with a three-speed automatic transmission; the standard transmission for all of the Skylark's engines.

The engine also has an attractive appearance under the hood. Lots of aluminum alloy castings and brightwork. And what isn't obvious is also impressive. The dual overhead camshafts are chain-driven; ignition is by computer-controlled coil ignition system; there are direct-acting hydraulic lifters, and a self-tensioning single accessory belt drive system reduces maintenance.

Another strong point of this engine is fuel mileage. The test car averaged 19 miles per gallon for city driving and 28 mpg over local highways. Because of the high 9.5:1 compression ratio, unleaded premium is recommended.

Fortunately, the Gran Touring suspension is up to handling the additional power. This system does contribute to a firmer ride but it is not the least bit stiff or harsh. The basic suspension features MacPherson struts up front and semi-independent trailing crank arms with coil springs in the rear.

Base price for the Skylark Limited sedan is $11,721. With a destination charge of $400 and a whole bunch of options, the bottom line on the test car came to $16,206. Options included air conditioning, $675; Quad 4, $660; 6- way power seat, $240; glass sunroof, $350; power door locks, $195; power windows, $285; electric trunk release, $50; intermittent windshield wipers, $55; rear window defogger, $145; designer accent paint, $195; cruise control, $175; tilt steering column, $125; concert sound, $100; graphic equalizer with cassette, $287; electronic cluster, $265; power antenna, $70, and several trim items. The price also reflected a $660 discount.

The car is covered by General Motors 6-year/60,000-mile powertrain warranty and 6-ye ar/100,000-mile outer-body rust-through protection.