"One of the '70s' most profitable business opportunities," is the way an advertisement in a specialty magazine describes it. It is a skateboard park.

Skatebaording is more than an old fad reborn. According to Skateboard magazine, it is an industry that did $300 million in nationwide sales last year.

The skateboard is ubiquitous. Every kid who wore a Redskin hat and jacket all winter is spending the summer on a flat piece of wood or plastic. Local governments grapple with the phenomenon, trying to decide where the fourwheel vehicles may and may not be ridden.

And that's where the skateboard park comes in.

Ron Wallace, a hairdresser at the Bethesda Ramada Inn beauty shop, first saw a park's potential when he read an article in a news magazine that quoted sales figures.

"That's a lot of money out there," Wallace said. "I wanted to get a piece of the action."

He sold the late James S. Long, chairman of Miller & Long Co. construction firm, on the idea of a park. Long went into it as a silent partner who could finance the venture, and in June 1976 the idea of Free Style Skateboard Park in Gaithersburg was born.

Wallace traveled up and down the East Coast, looking at other parks before he began to design Free Style with his next door neighbor, who is an architect.

When the two did begin the design, they had to to work within the limitations of the location they had found. The former miniature gold course is long and narrow, and a small freestanding building was already there. Wallace and his neighbor laid the park out around the building, which now serves as Wallace's pro shop.

Wallace estimates that the completed park, which opened in April of this year, cost between "70,000 and $80,000 to build.

In June, his third month of operation, Wallace saw Free Style generate $20,000 in revenues.

Of that $20,000, more than half comes from pro shop sales. Another quarter represents the hourly fees the skaters pay to use the park, and the remainder comes from equipment rental.

Wallace and Long were both lucky and smark. They built the first skateboard park in the Washington metropolitan area, and skaters from the entire area show up there every day of the week, from 10 a.m. to 11 p.m. (except Sundays, when it opens at 1 p.m.).

But they had bigger plans. "We were going to open this one and, boom! build another," Wallace said. "We'd have had it all signed up, Fairfax, Baltimore, Fredericksburg." Unfortunately, Long died in April and so did the big plans.

What is a skateboard park? It is a sea of concrete, frozen waves really. Skateboarders talk a modified surfer jargon. You may hear a group discussing great drainage ditches they have known, "still waves" to the initiated. Bridge embankments are another favorite.

A skateboard park has the attributes of both, and more. There are runs with banked curves of varying heights and steepness. There are big hills for the advanced skater to go flying over, and small ones on which the beginner can build confidence.

The big advantage of a skateboard park is safety. Park require skaters to wear protective equipment, including gloves, elbow pads, helmet and, if the skater is wearing short pants, knee pads. A skater who doesn't own safety equipment can rent it.

A Seat Pleasant woman sat just outside the fence surrounding the Gaithersburg park in the lawn chair she had brought with her. She was watching her 15-year-old son skate. He had heard that a park had opened recently and finally found it by calling the Maryland State Highway Patrol.

She commented on the safety precautions at the park. "We live on a hill and at home he rides up and down the sidewalk. But he doesn't wear all the safety equipment there. Here he has to wear it."

She seemed slightly bemused by the whole phenomenon. "His father bought him a board for about $40. The before long he needed four new wheels, at $10 a piece. He probably has $100 in his board by now. Then for his birthday, his father bought him all the safety equipment. Now he gets a skateboard magazine and he's asked me how far it is to drive to New Jersey" where there are other skateboard parks.

"I'm glad this is what he's going," the woman continued. "He's always been active in sports."

But the woman had one problem. She had brought her son all the way from Seat Pleasant, so it only made sense for her to sit there in her lawn chair, watching and waiting for him. But she would have been happier if she could have been shopping while she waited.

Sidewalk Surfparks, Inc., may have the answer for her. That company plans to develop a $300,000, two-acre park across from the White Flint Mall.

An opening date has yet to set and construction has not begun. The company still must obtain the necessary permits and approvals from Montgomery County although rezoning is not necessary.

Sidewalk Surfparks is headed by Richard Ault and it includes Charles Roberts and Jimmy Finigan. Roberts and Finigan also own the Bethesda Surf Shop in Bethesda and Sunshire House in Ocean City.

Both stores sell surfing and skateboard equipment. Roberts estimates that a quarter of the Ocean City store's sales comes from skateboards, while perhaps 65 per cents of the Bethesda shop's revenues is from skateboards and related equipment.

Roberts would rather not reveal sales and profit figures. He will say, though, that prior to 1974 his skateboard sales were nominal. That year, however, saw the tremendous growth of the sport in the East, and in 1974 Roberts and Finigan saw their sales increase by more than 100 per cent. Their sales have increased an average of 20 per cent each year since then. Projections for 1977 are similar.

Skateboarding came to life again on the East Coast in 1974 primarily because someone decided that skateboards shouldn't use clay wheels as skates do. Clay wheel stop when they run across a minor obstacle such as a bottle cap or a stone. When the wheels stop suddenly, the skater is thrown off.

Then along came the polyurethane wheel. The plastic wheels, softer than clay ones, could absorb minor impediments and leave the skater in control. The axle and steering assembly, called a truck, was designed with greater sophistication. The entire product was made with greater precision, and permitted a skilled skater to "get radical" on the "concrete waves" and make more daring maneuvers.

So skateboarding, which never died out in California the way it did here, began creeping back to the East with growing popularity.

Though skateboarding is a young sport, it has its myths and legends. One of those legends is that the clever person who though of making polyurethane wheels "was a young guy about 25 who poured them (the wheels) in his garage and now he's rich." The legend is unconfirmed. It has been confirmed, however, that most skaters are young.

The sophistication of design that separates the skateboard of today from the skateboard of ten years ago also separates the prices.

Ten years ago, he who had a $20 skateboard was a big spender. Now, the average price for "good equipment" is $80, according to Bethesda Surf Shop manager Bill Barrett. Prices can range from $15 to $130.

The safety equipment runs another $40. A shoe with a polyurethane sole soon will be marketed.

And what is sport without tee shirts? The skater who has a favorite brand of equipment can inform his fellow skaters of his preference by buying a tee shirt with the company's logo on it.

There are even skateboard professionals. Their activities, like the entire industry, are centered primarily in California.

The pros work for manufacturers. They use and endorse their employer's equipment, enter organized competitions and give demonstrations.

Henry Hester, who was interviewed for the July issue of Skateboarder magazine, said "I'm making about $1,400 a month. That's not including royalties."

Will skateboarding go away again, as it did before? No one seems to think it will any time soon.

"There were 3 million skateboards sold last year," Barrett said. "It hasn't peaked yet. I thought it was peaking a couple of years ago, but now it's not even close."

The design sophistication has made the skateboard both more versatile and safe. According to Barrett, that means "skateboarding is going to be around for a long time."

Is Wallace optimistic? "The East Coast is going crackers," he said. "What's next? Europe. Build a skateboard park in Europe if you want to make bucks!"