PROFESSIONAL beach-volleyball players are a homogeneous group. They're all at least six-feet tall, tanned, and muscled. Almost every one claims southern California, the cradle of beach volleyball, as home.Many of these athletes remember when the game was played "for a handshake and a trophy," as top-ranked player Randy Stoklos puts it. Today, the young sport boasts a 24-city nationwide tour and $2.6 million in prize money. It will be an "exhibition" sport at the 1992 Olympics. From its humble beginnings among American World War I soldiers who played volleyball on the sand for recreation, beach volleyball became a casual pastime of pick-up games between young "beach bums" on obscure southern California beaches. In 1976, the sport went professional with the first World Championships of Beach Volleyball in Pacific Palisades, Calif. The total prize money was then $5,000. Now, weekend-long double-elimination tournaments offer a minimum of $65,000 in prize money. The tour is entirely funded by corporate sponsors. Karch Kiraly, two-time Olympic gold medalist in indoor, hard-court volleyball competition, first learned to spike the ball on the sand. "I started on the beach in Santa Barbara with my father when I was six," he says. In fact, Mr. Kiraly prefers playing beach volleyball to indoor competition. "It's more challenging on the beach," he says. "And there's a totally different atmosphere. There's not nearly so much protocol as indoors. It's not so strait-laced." The tournaments strike a casual observer as little more than one giant beach party. The commercial barrage is relentless: Beer companies and sportswear manufacturers are major supporters [see adjoining article]. But for the top players this is not only sport, but business. The best two-man teams earn more than $200,000 in prize money over the eight-month season. And contracts with sportswear companies augment those healthy earnings. Many of the players walk around so plastered with brand names that they look like human stock cars. Mr. Stoklos, who is under contract with a sportswear company, won't step on a court without stopping to don a FILA headband. "That's part of the sport now," Kiraly explains. "That's how it's evolved." RATHER than the traditional six-player teams of indoor volleyball, pro beach volleyball pits teams of two against each other. The sand court on the beach is the same size as indoors. But with three times as much territory to cover per player and slippery, often blazing-hot footing, beach volleyball is a faster game. Despite having only two-man teams, the rules are basically the same as the indoor version. Tournament matches are decided by one game played to 15 points rather than the best 3 out of 5 games played to 15 indoors. Players can serve anywhere across the back line rather than being confined to the right corner. Many of the players switch teammates frequently, constantly looking for the right combination of skills and interaction. But the No. 1 team of Stoklos and Christopher St. John (Sinjin) Smith have been together for ten years. "It's like a marriage," Stoklos says of the team. "But, more importantly, we make a living together." Pro beach volleyball is expanding its reach beyond the coasts. At inland locations, the tour hauls in sand to create its own artificial beach and sand courts. This year, the tour brings its beach to landlocked cities in Texas, Pennsylvania, and Ohio. Up to 10,000 people fill the bleachers at each stop. Kiraly gives two explanations for the explosive popularity of pro beach volleyball. First, he says, the success of the US men's indoor volleyball team at the 1984 and 1988 Olympics gave its beach-side counterpart a boost. And he credits increased TV exposure with helping beach volleyball gain a following. All 24 of this year's tournaments will be nationally televised. Prime Network and ESPN broadcast most of the tour stops, and NBC has just agreed to air three of the events live this season. Stoklos has a simpler explanation for the sport's popularity. "Everybody wants to be part of the California lifestyle," he says. "It's an easy sell." But the players know that their audience isn't just there to see the action on the court. "That's what is attractive about it," says Kiraly. Admission is free and anyone on the beach can stop by for a few minutes of sun and fun with the added entertainment of an exciting game. "For all the spectators, it's a happening," Stoklos says. In most locations, the event includes a swimsuit competition featuring bikini-clad women who parade across a stage for a panel of community judges. "When this started, that was just part of the package to draw people in," says Sam Lagana, announcer for the tour and emcee of the swimsuit competition. He admits that some people find it offensive and says: "Imminently, I think it will go [by the] wayside." Mr. Lagana has been the tour's announcer for seven years. ve been with this sport since it was this big," he says, putting his fingers an inch apart. "And now it's this big," he adds, stretching his arms as far as possible. Part of the thrill, Lagana says, is that volleyball is one of the few sports invented here in the United States. Some players on the tour hold down professional jobs - including at least one lawyer, stock broker, architect, and teacher. Other players dedicate their entire life to the beach. On the tour's four months off, what does Randy Stoklos like to do? "I just go down to the beach and surf."