VERNON HEIGHTFIELD didn't mean to reinvent the wheel. The urethane rubber he was experimenting with in 1970 was supposed to be for a new pipeline system.

But being as good a father as he was a scientist, the Purcellville, Va., inventor gave in to his young son's pleas and poured the sticky stuff into four wheels for a makeshift skateboard.

Skateboarding was reborn.

The wheels' unique texture created entirely new possibilities for durability, maneuverability and speed.Frank Nasworthy, a determined young employee at Heightfield's Creative Urethane Plant, spent the next three years marketing his own versions of the super wheel on the West Coast and by 1975, youthful riders throughout the country were doing popouts, powerslides and kick flips.

The stunts seemed limitless and suddenly so did the injuries. Today the fact is, if you ride a skateboard - sooner or later and probably sooner - you're going to fall off of it.

Despite the risks, the skateboarding industry grossed over $300 million in the United States last year. Skateboard competitions, new publications and the handful of skate parks in existence are thriving. Fortunately, the refinement of skateboard components and the production of safety equipment have kept pace. These advances may not keep you from falling but they can reduce the chances of getting hurt.

Here are a few dos and don'ts for those brave enough, wild enough and young enough to entertain notions of skateboard mastery:

Many stores sell skateboards, but specialty shops have the widest selection and usually offer warranties on individual components. At these stores you generally are dealing with people who have skateboarding experience. They can advise you whether to buy a presassembled board or can help you pick separate parts so you can put your own board together.

WHEELS ($2 to $12.95 a pair): A major drawback in skateboards of the 1960s was the clay-compound roller skate wheel. The surface was too hard to take bumps. The urethane wheel rolls over pebbles or rough asphalt without tipping the rider.

There are three wheel variables to consider - texture, size and shape.

The harder the wheel, the less traction and the more speed. Conversely, softer-texture wheels held more with ground surface, giving more control.

Bonus Tip: Wheel texture is measured in terms of a durometer rating on a scale of 0-100. Find out what that rating is. Beginners should avoid anything harder than 85.

Size and shape affect both speed and mobility. A smaller wheel is slower because it covers less ground per rotation; similarly, a wide wheel is slower than a thin one because there is more surface friction. In general, the taller and thinner wheel best for downhill speed events.

The outer edges of wheels also vary and are an important consideration. A thin outer edge grips the ground hard on turns and provides a slower though, sometimes choppier ride. The rounded, 'barrelled-out' edge is preferred by many skateboarders because of its ability to take turns quickly, smooth and sharply. This wheel is especially good for stunts and slalom competition.

Bonus Tip: If you're a beginner, there's no need to buy a wheel that is primarily suited for speed or trick riding. Look for a small to medium wheel with a slightly sharp outer edge. As you progress, the edge will barrel-out on its own. Then think about moving up to a more advanced wheel.

Bonus Tip: Look for precision bearings, enclosed in a cylindrical metal case so they won't get dirty or fall out. They require no maintenance.

TRUCKS ($2.50 to $24.95 each): Each skateboard has two trucks to hold the axles and permit steering. The earliest 'Chicago' trucks for roller skates had and required little mobility, but trucks today feature diagonal and sometimes up and down movement.

The "Stoker," possibly the most advanced truck on the market, resembles the underside of a car, with parts that act as shock absorbers, pivots and a stress plate. This truck is best suited to tall, fast wheels and competent riders.

Bonus Tip: A beginner may not need a Stroker but should want a truck with adequate two-way mobility. Be equally concerned with the truck's strength because the skateboard's stability depends on it. High grades of steel are now used to insure safety. Also, check to see how the stress plate is anchored to the board. The stronger the screws and the more there are, the less chance the truck will break loose.

BOARDS ($9 to $60): There are a variety of board types and choosing one really comes down to individual preference:

Plastic is the least sturdy and is basically for children's skateboards - no fancy stuff.

Fiberglass is generally the next step up in price. Fiberglass boards are light but strong. They tend also to be quick and may throw a beginner off balance.

Wood is still the most widely used because of its sturdiness and versatility. Some wood boards can chip, but generally that is not a problem.

An aluminum board is good for tricks, but if it is run into curbs the edges get sharp and may be hazardous.

Wood laminates are best and most often used by professionals. The 'all-wood' is made of several kinds of strong wood, looks slick and is very light and durable.

Other laminates are designed for specific events in competition. 'Wood-inside-aluminum' is flexible and good for slalom. 'Plexiglass/wood' is good for freestyle because it's light.

Bonus Tip: Board size is not a matter of preference. If you're 5-foot-5 or under, go for a 24- to 26-inch board; anything longer will be hard to maneuver. The most popular boards are 27 to 29 inches long. The long 36- to 44-inch boards are for speed racing.

SAFETY EQUIPMENT: Protective gear is essential, required in skate parks and endorsed by the American Skateboard Association.

Helmets come in all shapes and designs. The least expensive is a $7.95 model approved by the National Hockey Association. It is sufficent for recreational skateboarding but if you'd rather play it safer, a $12.95 helmet is available which has more foam padding and covers the back of the head.

Pads are vital and must fit properly to save your elbows and knees. Most are the slip-on variety and must be snug enough not to slide up the arm or leg they're supposed to protect.

There are a half-dozen kinds of gloves and you'll need one of them to protect your hands. The best have protective palm cushions already sewn in. Some skateboarders prefer a plastic plate that straps onto the hand and helps you slide through a fall.

THE LAW: Local ordinances differ from jurisdiction to jurisdiction. In Montgomery County there is no regulation of the sport but police are cracking down on parking lot and shopping center riders. Field interrogation tickets are being issued, alerting parents to potential skateboard troubles. Skateboards can be temporarily impounded in Montgomery.

In Prince George's County there is no law for skateboards, no tickets are issued but police will stop and lecture negligent riders and keep them off private property. Skateboards are banned from all streets in the District of Columbia by pedestrian laws. A Virginia state law prohibits all roller skates and play vehicles from the streets.

SKATE PARKS: These enclosed skateboarding arenas, resembling asphalt sand dunes, originated in California but have now begun to sprout in the East. The only local park is in Gaithersburg - Free Style Park, a privately run operation where $2.25 gets you two hours of skateboarding and $3.50 lets you d o it all day.

The city of Bowie is considering converting an ice rink into a skateboard park for six months a year.

According to a spokesman for the Ocean City Police Department, "the number of skateboard incidents and accidents has really declined since we built our skate park two years ago. It gives the kids some place to go and they have to use safety equipment there or they can't get in."

So, the skateboard boom continues. Inevitably, the risks do too.

"I treat around five skateboard-related injuries a week during the summer season," said Dr. William Moore, an orthopedist in the Salisbury/Ocean City area.

"They range anywhere from abrasions to broken wrists and ankles. For youngsters, bone breaks can be serious because anytime you have a fracture near a joint there's a propensity for growth problems. Adults have to be careful, too. Always check out a sprain because it might be a slight fracture. It could lead to arthritis."

"But you have to put it into perspective," Moore added. "There are a lot of things you do in life where you many get hurt - bicycles, swings, little leagues. You can't go through life in a shell. I ski. If you want to skateboard, do it. Just do it sensibly."