The full beauty of a full-size 4 by 4 utility vehicle can't really be appreciated until you drive one through several snowstorms. You sit tall in the saddle and, while you may not be away from the maddening crowd of other vehicles, there is a certain amount of isolation felt from the very secure and home-like atmosphere surrounding you.

No doubt about it, when the going gets tough, the tough gets full-size 4 by 4 utility vehicles. The rest of the year, though, could be somewhat of a different story. After all, driving over dry roads in the sunshine doesn't really require any special type of vehicle. The big utility vehicle could be a car for all seasons but winter should have an asterisk after it.

The big utility vehicle did come on hard times in the 1970s as gasoline prices gushed up. It was never a vehicle designed for fuel economy, and manufacturers were really caught off guard with the mood of the times and consequently this vehicle never really recovered its former popularity. However, in the past couple of years there has been a steady climb in sales. This is rather interesting when you consider that the big utility vehicle manufacturers themselves cut into sales with the introduction of compact utility vehicles. It probably has something to do with those consumers who think that big is better.

Anyway, we still have the full-size utility vehicle with us. And this week we will review the Chevrolet Blazer, which, for years, has been one of the most popular utility vehicle. But, then, it does have that Chevy bow-tie on it and that never did hurt sales.

The test vehicle (supplied by Scott Chevrolet, 3333 Lehigh St., Emmaus) was driven during a period of ideal four-wheel drive conditions - lots of snow, lots of slush, lots of water and just enough ice thrown in to make things interesting. There was no stopping in the woods on a snowy evening with the Blazer. It just kept going and going and going.

Preppies and young children will probably take one look at the Blazer and say ''awesome.'' It is very high (over 6 feet), very wide (about 6 1/2 feet but counting the outside mirrors close to 8) and relatively long (over 15 feet). The wheelbase measures 106.5 inches and curb weight comes in at 4,444 pounds. There is sort of an overall no nonsense look about it. Styling is similar to last year's, which is similar to years before that.

The interior has sort of a small cave look to it. What you see on the outside is what you get on the inside. There is seating for five and you could certainly throw a couple of people in the cargo area behind the rear seat, if you were so inclined. The test vehicle's seats were covered in a vinyl material that felt tough enough to resist an attack from a school of bluefish. (What a school of bluefish is doing in a Blazer is this week's riddle.) Vinyl, though it can get very cold on a frosty winter night, is a good choice for those who are going to combine their outdoor activities with this vehicle. In other words, you can clean it up as fast as you can mess it up. But for those with more genteel demands, cloth material is available. Something new for 1986 is molded front bucket seats with folding seat backs. Also, the passenger seat has a slide-forward, easy-entry feature that has been standard on the smaller S-10 series.

The high driving position provides good all-around visibility, which, in turn, makes the Blazer a relatively easy vehicle to drive. The relatively short wheelbase is most appreciated in tight maneuvering and parking. The only thing one has to get used to is the width. As noted before the Blazer is very wide. Aside from the width, the Blazer is a real pussycat to drive. (It may look macho but women and wimps will have no problem running it on or off the road.)

Another sort of surprise is that the Blazer actually gives a decent ride. This is something when y u consider that the Blazer uses leaf springs on semi- floating axles both rear and front. (Really the same framework as Chevy's 4 by 4 half-ton trucks.) It is a ruggedly built vehicle. But then when you consider that one of its big selling points is heavy-duty towing, it shouldn't come as a surprise. In fact, Chevy says a properly equipped Blazer can move up to 11,000 pounds, including vehicle, passengers, cargo, equipment and trailer.

The test vehicle was equipped with automatic locking hubs which meant that it could be shifted into four-wheel drive High at speeds up to 25 mph - without even leaving the cab. (Manual locking hubs are standard.) Very easy to operate.

Powering the test vehicle was a 5.0 liter/305 cubic inch V-8 with four- barrel carburetor. This engine has powered many Chevy and General Motors vehicles and has an excellent reputation for reliability and ruggedness. The version in the Blazer is rated at 160 horsepower at 4,400 pounds and 235 foot pounds torque at 1,600 rpm. Performance was good for all Lehigh Valley driving conditions. The test vehicle had the optional four-speed automatic transmission (a four-speed manual is standard) which has an overdrive fourth. Although by no means an economy vehicle, the transmission certainly helps fuel mileage. The test vehicle averaged 9 miles per gallon for city driving and 15 mpg over the highways. For a full-size utility vehicle this isn't bad, especially when you consider the conditions the test vehicle was driven though.

For those people interested in such things, there is an optional diesel engine available. This engine measures 6.2 liter/379 cubic inches and is rated at 130 horsepower at 3,600 rpm and 240 foot pounds torque at 2,000 rpm.

Total price for the test vehicle came to $17,669, including a destination charge of $525. The base was $12,034 and included such standard items as power brakes, power steering, tinted glass, dual outside mirrors, chrome bumpers, steel-belted all-season radials and a nice level of trim. Options included sliding side quarter windows, $243; folding rear seat, $369; air conditioning, $740; electronic speed control, $195; four-speed automatic, $695; tilt steering wheel, $115; 31 gallon fuel tank, $115; Am-FM stereo with cassette, $298; weight distributing platform hitch, $155; Silverado equipment (dress up package), $1,015, and exterior decor package, $314.