When Rain Bou Runner on desperately to win the fifth race at Gulfstream Park, Ron Hansen turned to his companions and ammounced: "It's all over. I'm a winner." He cared little that if he were right he would be dashing the hopes and dreams of thousands of other bettors.

What Hansen thought he was about to win was Gulfstream's new gimmick bet, the Super Six with Jackpot. In an era when high-paying exotic wagers have abounded at tracks across the nation, there has never been a bet so compelling and hypnotic. Even grizzled, blase race trackers find themselves dreaming about the Super Six or waking up in the middle of the night to handicap it one more time.

The Super Six requires bettors to pick the winners of the second through the seventh races; it is essentially the same gimmick that proved a sensation in California but flopped in Maryland and most other states. But Florida instituted it with a new wrinkle: If nobody picks all the winners, half the money in the wagering pool goes into a jackpot that builds until someone does hit six in a row.

Horseplayers here were indifferent to the Super Six (as were bettors at Laurel) when the total daily pool was only $12,000 or so. But as days passed, with nobody going six for six, the jackpot grew progressively.

On Thursday, the pot had built to $60,000, and The Washington Post's racing columnist thought he was about to enjoy an early retirement when he hit the first three winners at 6-5, 16-1 and 9-2 and held a multiplicity of live tickets, but longshots eventually eliminated everybody. On Friday the jackpot had grown to $81,000, and any gambler with the slightest comprehension of odds felt compelled to play.

Hansen has considerable comprehension of odds. He had been playing horses since he was a tot growing up in Chicago, and had been a serious student of the game for a quarter-century. He had worked in the meatpacking business and done investing in real estate, but since settling in Miami, Hansen had been a more of less full-time professional gambler.

Hansen had always loved gimmick bets, and his interest was piqued last year when Hollywood Park's new Pick Six started to attract enormous betting pools. In April, when the bet portion of the Florida season was finished, he headed to California. "For two weeks I just sat and watched," he said. "The third week I started playing. I was putting $500 to $800 a day into the Pick Six. In three months I collected a total of about $300,000. The big one was $87,000."

So when the Super Six jackpot reached a record level on Friday, Hansen stepped into action. He bought a ticket costing $1,152, using from two to four horses in each of the races. His choices weren't especially exotic; he used solid, logical horses, mostly favorites sprinkled with a few longshots. Obvious horses won the second and third races, but when the fourth race was won by a 21-to-1 shot in whom Hansen had perceived some virtues, he knew he had an excellent shot for a killing. He had one worry: the next race.

A late scratch had left him with only one horse in the field, Rain Bou Runner, who was favored but had shown some signs of having a weak heart. Hansen watched with concern as the horse tried but failed to get by the early leaders on the backstretch. But soon the horses around him started collapsing, and Rain Bou Runner managed to outstagger them to the wire.

That was the moment when Hansen announced, "It's all over." He was premature but just barely. He had three solid horses in each of the next two races, and when favorites won them both easily, he waited calmly to learn whether he had to share the pot with anyone. He didn't; his ticket was worth $130,700.

Hansen did not even let out a whoop. He went to the Gulfstream mutuels department and calmly filled out his tax forms. When the track photographer took his picture for the morning papers, he had to ask twice that Hansen smile for the shot. Having fulfilled that obligation, the winner stuck his check for $104,560.80 into the pocket of his blue jeans and left to await the next big Super Six jackpot.