Nearly 100 young skateboard enthusiasts turned out yesterday afternoon under a blazing sun to test their skills in Prince George's County's first skateboard tournament.

The tournament, sponsored by the Bowie Jaycees, included skateboard races down a 200-yard-long hill, slalom racing, and competition involving skateboard stunt riding.

Skateboarding apparently has surpassed soapbox derby racing as the favorite of youthful racers, according to Jaycees president Barry L. Mones. The Jaycees decided this year to put on a skateboard tournament - in concert with Bel Air Skateboard Co. - rather than sponsor another derby, because interest in the derbies had been flagging in recent years, he said.

Yesterday the contestants in their knee pads and crash helmets, some of whom paid up to $100 for their special racing skateboards, rode the asphalt waves at speeds of up to 40 miles an hour.

The revolution in the popularity of the sport, which once was based on cannibalized steel roller skates attached to the bottom of a plywood board, is attributed by enthusiasts to the development of special wheels and flexible boards that enable the rider to manuever with greater ease and confidence.

Most of the participants, many of them toting skateboards under their arms, pointed out 21-year-old Steve Nelson of Bowie as the best competitor there yesterday. Nelson, who said he has "scabs from head to toe" from skateboard tumbles, said he started skateboarding two years ago. In yesterday's competition he won trohpies for speed and slalom racing.

Richard Harrison, 14, of Bowie had been practicing for nearly a week in an effort to win a prize in the speed skateboarding competition. He said he was a little nervous as he approached the starting line on Bowie Race Course Road. But then the gun sounded and he quickly jumped on the board and was off.

Harrison's plans was to throw his arms out in front of him as he approached the finish line. His calculated move cut a fraction of a second off his time but also threw him off balance and he tumbled across the finish line. Nursing a bruised arm, he stood up and waved to the crowd of nearly 500. But his tactic failed to win him a prize.

One skateboarder said the whole afternoon was "fun, and a sport like this keeps us kids on the streets."

As the youngsters raced down the sloping hill and others tested their skill on a 10-foot ramp, sometimes falling or shooting their skateboards into the crowd, Bowie Jaycee president Mones said. "It is comforting to know that that man over there is our insurance agent."