Of the 90 horseplayers entered in the finals of the World Series of Handicapping at Penn National Race Course, Jack Sloan probably felt most at home in the environment. Sloan earns his betting money by working as a nurse in a psychiatric ward.

If the typical race track crowd consists of a bunch of intense, monomaniacal eccentrics, the entrants in this three-day contest were even more intense, more monomaniacal and more eccentric. Their purposefulness was understandable. Each started on Friday with a mythical $1,000 bankroll with which to bet over the next three days. Whoever amassed the largest mythical total would win a very real first prize of $45,000.

The field consisted of 30 invited "experts," mostly from the media, and 60 horseplayers who had emerged from preliminary qualifying rounds held earlier in the year. They were a heterogeneous lot.

Cam Ying Chan started playing the horses when he was a high school principal in Hong Kong, then adapted his handicapping methods when he moved to New York. "It's same thing but different horses. I find horses who figure. Never bet favorite. Never."

Norman Walesczak, a quiet man from Cheektowaga, N.Y., said this was the first time he had been in a contest in a quarter-century. "In 1957," he said, "I was in a talking contest and I talked for 82 hours straight. I got beaten by a woman. Naturally."

Sherman Brown had good reason to want to win the first prize. He is in the nonbooming real estate business, and he has two kids starting in college this year. When his son was admitted to Drexel (tuition: $6,500) he sent in his entry to the World Series of Handicapping.

Most of the contestants bet cautiously on Friday night, but on Saturday Sloan made a decisive move. One of Penn National's top trainers, Bruce Kravets, had entered a horse named Shanghi Eddie in the first race and was using an obscure jockey named Tom Jaramillo. "I spent an hour researching Jaramillo," Sloan said. "I found out that he had ridden for Kravets once and won for him once." Sloan bet $400 of his bankroll, and he was shouting "There's a new leader in the clubhouse!" as he watched Shanghi Eddie draw off to win at 7 to 1.

Sloan had a chance to realize his great goal: fulfilling himself as a horseplayer. "Six months ago," he said, "I started working nights so I could go to the track full time. I've been very streaky. I'm behind. But if I win this contest, I'm going to send my boss a four-word telegram. It will say: "I WON. I QUIT."

Sloan stayed in first place until Woodbine Billy made his move later that evening.

Bill Gilbert had qualified for this contest by winning a similar event at Woodbine Race Track in Toronto, and his victory was no fluke. "He's very reclusive; you can hardly talk to him," said a fellow Canadian. "He lives and breathes horses. Two years ago he won the Woodbine contest, too, but he declined to come to Penn National. He said he had too many good winners coming up at Woodbine and it would cost him money to leave."

Woodbine Billy bet $400 to win on an 8-to-1 shot named Contrato to take over first place, and Vincent Francia, the track public relations director, asked him why he had chosen that horse. "That's a secret I can't divulge," Woodbine Billy said. "Actually, a Chinese friend of mine in Canada told me any time I had a bet coming up, 'Wash your feet.' I know you won't believe that. Just print that tomorrow is a long day."

"I felt like I was talking to a Tibetan monk," the p.r. man said.

Woodbine Billy maintained his lead into the final race on Sunday afternoon, as most of his rivals took big shots and missed. Sloan's bankroll had diminished. The Washington Post's two entrants had long since gone broke. Now the survivors were all taking last shots, trying to hit a horse at a decent price. Most of them settled on a horse named Saint Nicholas. Three of them -- Sloan, Brown, and 19-year-old Ronald Yascavage -- went for Battered n Bruised.

"I'd been waiting all day for this horse," said Brown, the real estate man who had been playing the horses in New England most of his adult life. "I basically pay attention to the speed figures in the Racing Form, and I like to bet horses changing distance. Battered n Bruised had the best speed ratings at six furlongs and now he was going a mile."

Brown bet $800 on Battered n Bruised; Yascavage, who was considerably ahead of him in the standings, bet $500 to win, $200 to place and $100 to show on the horse. So when Battered n Bruised drew off to a nine-length victory, Brown said, "I was very happy. I thought I'd come in second." The $15,000 second-place money would pay a lot of tuition bills.

Then the prices for the winner flashed on the tote board; he paid $15.20, $4.40 and $3.00 across the board. Yascavage's place and show bets had returned him surprisingly little. When contest officials pushed the buttons on their calculators they found that Brown had wound up with a total of $6,080, while Yascavage had $6,066. Sloan came in third and Woodbine Billy was fourth.

If Battered n Bruised had paid just 20 cents more to place, Brown would not have won. As he collected his check for $45,000, he could reflect that in the World Series of Handicapping, as in the real world of handicapping, it helps to have one's skill augmented by a little bit of luck.