In the midst of chaos at Exhibition Park, a little racetrack in Vancouver, Peter Wall remained calm.

Record crowds had been jamming the track and straining its capacity last week, with everybody in pursuit of the same thing: the possibility of collecting the largest payoff in North American parimutuel history. Wall shared their ambition but not their freneticism. "I really thought I'd win it," he said flatly.

The source of the excitement was the Sweep Six, a form of wagering that Exhibition Park initiated this spring. The object is to pick the winners of six consecutive races, the fourth through the ninth, and if nobody accomplishes this feat the entire betting pool is carried over until the next day.

After eluding bettors for three nights, the pot had grown to $500,000 a week ago Monday. On Wednesday, it was up to $992,000. Vancouver was going wild. "You couldn't buy a Racing Form anywhere," said Harry Filion, the track's publicity director. "It was a front-page story in all the local papers. On Friday night, all the TV networks were at the track. We haven't had so much excitement since Johnny Longden rode his 6,000th winner here."

On Friday, 21,000 people came to the track, betting nearly $1 million on the Sweep Six, but only one ticketholder hit the first five races. With a chance to collect a seven-figure payoff, this anonymous soul watched his horse take the early lead, only to fade and finish last. Now more than $1.6 million was being carried over to Saturday night. This was the night that Peter Wall decided was going to be his.

Wall is a prosperous Vancouver real estate man with a moderate-sized breeding and racing operation in California. Ordinarily, he doesn't play the horses much at his hometown track because the small wagering pools don't permit betting on a serious level. But this was clearly a different situation.

"I called a friend of mine in California who has won the Pick Six there several times," Wall said. "I discussed it with him and came to the same conclusion: you concentrate on eliminating horses. You've got to narrow at least a couple of the races to one or two horses. You look for hard-knocking horses who know how to win."

Wall had been playing the Sweep Six as the pool grew, but his bankroll gave him more staying power than some of the other local horseplayers. On Saturday night, only about $550,000 was bet on the Sweep Six. Filion theorized, "There was no chance for office syndicates to get together, and the banks were closed. Besides, I think we also broke a bunch of people on Friday."

So on Saturday night, Wall marked all his Sweep Six choices on a ticket that he said cost him "between $10,000 and $20,000." Some friends bought 2 or 3 or 5 percent interests in the ticket, but he remained the majority stockholder. He felt that all he needed was six reasonably logical results to be a winner.

A 7-to-1 shot won the first race in the Sweep Six, followed by winners at 5 to 2, 3 to 1 and 9 to 2. Wall had them all, and felt that his only remaining worry was the fifth race, where he had three horses in a tough, competitive field. One of Wall's choices, Here's Your Ticket, was being stalked by a horse he hadn't used, Mr. Docile, and he watched with concern as Here's Your Ticket began to weaken.

"As Here's Your Ticket stopped," Wall said, "he intimidated Mr. Docile a bit. And as he did, another of our horses, Partner J.R., came on. He won by a head, with some luck. I don't think he was the best. But after that race, I was quite confident that we would win. We were well-covered, and had the four favorites in the last race."

Wall's confidence was justified. One of his horses, No Vices, won with ease at 4 to 1. What gave him even more pleasure was the announcement shortly thereafter that there were only three winnings tickets on the Sweep Six. "I was very surprised," he said. "If this had been in California, five or 10 people would have had it. This was not a difficult card."

Having to share the $2.2 million pot with only two other bettors, Wall went to the cashier's window and received a check for $735,403, which is believed to be the largest payoff in the history of the sport.

And that was only part of his good fortune. The other part is that he happened to collect his windfall in a civilized country that imposes no taxes on gambling winnings.