Lou Guida is happy, for many reasons, that he got out of the stock-brokerage business to devote full time to harness racing.

He hasn't had to worry about the recent upheavals on Wall Street. Instead, he has been able to enjoy his phenomenal streak of success in the standardbred game. Guida has owned the harness horse of the year four times since 1980 and could win his fifth title with Mack Lobell, the fastest trotter in history, who races at Rosecroft tonight.

"In the stock market," Guida said, "you can be the smartest person in the world and things beyond your control can wipe you. In the horse business, you have a lot more control over your own destiny. A bomb falling on the Persian Gulf isn't going to make Mack Lobell go any faster or slower."

Guida has controlled his own destiny in harness racing so effectively that he seems almost immune to the normal vicissitudes of the business.

The personal odyssey that led Guida into harness racing began in a car wash he owned. One day, when he tried to prevent a new Cadillac from being hit from behind, his foot got caught in the conveyor belt and dragged him through the car wash. The owner of the Cadillac was the manager of a Merrill Lynch office, and he convinced Guida that the securities business would be a lot easier and safer.

Guida became a highly successful stockbroker and eventually a senior vice president of Merrill Lynch, earning enough money to take a plunge in harness racing. He lost a bundle on his first venture, decided he needed to study the business more extensively, and then took a plunge again.

When his colt Niatross became a champion in 1979 and paced the fastest mile in history (1:49 1/5), Guida was on his way to dominating the sport -- not only because of the performance of his horses, but because of the way he syndicated them.

"When I went into the standardbred business," Guida said, "they didn't have any idea about syndicating horses. It was easy for me because of my experience in the financial markets. It used to be that you couldn't get in on a good horse unless you were one of the 'good old boys.' I'd take a good horse and sell shares to 40 different owners, and I went the other direction from the good old boys. I'd sell to guys who had never had a chance to get into a good horse before."

Guida is clearly not a man who lacks in self-confidence, and his brashness has irked plenty of the good old boys in what used to be a very cliquish sport.

"A lot of people don't like me," Guida conceded. "They say I haven't paid my dues. I remember one time I was in the winner's circle with Nihilator {a son of Niatross} and a man came up to me and said, 'You're pretty lucky with pacers. You ought to try racing trotters and find out how much you don't know.' "

Goaded by that remark, Guida bought for $17,000 the trotter who is recognized now as one of the best of all time. The way he picked Mack Lobell illustrates his approach to the game.

"I've never met an investor who made serious money without a real conviction," Guida said. And Guida had a conviction about a stallion named Mystic Park.

"When he was a 3-year-old, Mystic Park was as great a trotter as I've ever seen," Guida said. "But he was raced when was lame, raced on the outside, raced against older horses and so the industry misjudged him because he didn't look good on paper. If he passed his characteristics on, I wanted to buy his offspring. I made a public announcement that I was going to buy every Mystic Park I could with the right conformation and the right blood crosses in his pedigree."

Guida bought Mack Lobell at a sale in New Jersey. The colt was voted the country's champion 2-year-old trotter last year, and has had an even more spectacular campaign this year. He won his two heats of the Hambletonian by a combined total of 12 lengths. He trotted a mile in a record 1:52 1/5 -- breaking the world mark by more than a second.

He missed the Triple Crown of trotting when Napoletano edged him in the Kentucky Futurity earlier this month, but he will have a chance for revenge soon. Mack Lobell will face his arch rival in the Colonial Trot at Rosecroft next Saturday. His race tonight is a tuneup for that confrontation.

Although it might be logical to retire Mack Lobell at the end of this season, Guida said he is considering another course. "I'd like to race him in Europe," Guida said. "The horses there are bigger and stronger than ours, and I'd like to show that he could beat the best European trotters."

Guida conceded it would be economically sounder to send Mack Lobell to stud, but he may find it hard to resist the challenge of conquering a new world.