All week long, Leon Blusiewicz had been telling his friends that they could make the biggest bets of their lives on Saturday, that his filly Snow Plow was a cinch to win the Selima Stakes.

Skeptics could recall hearing the exuberant Lou Blue talk this way before. Harsher critics thought he was crazy to enter an unseasoned 2-year-old who had raced only once in her life in a $210,835 stakes race.

But yesterday at Laurel, Blusiewicz had his vindication and his triumph, as he watched Snow Plow draw away to a decisive 2 1/4-length victory over Ambassador of Luck. Larida, the 3-to-5 favorite, faded to finish fourth.

Blusiewicz, who has been training horses in Maryland since he retired from a career as a seaman 12 years ago, bought Snow Plow for $35,000 at a yearling sale. He saw signs of great precocity in the filly earlier this spring, but he waited until October to send her to New York for her racing debut.

Did he bet that day? "Is the Pope Catholic? That's the name of the game," Blusiewicz replied. Snow Plow won that day at 3 to 1, and subsequently trained very fast, encouraging her owner-trainer to spend $8,850 to enter her in the futurity.

Her task seemed very formidable, since the regally bred Larida had won both her starts in New York by impressive margins and had the look of a future champion. Snow Plow's chances did not look much better after the race had begun.

Ambassador of Luck, with the legendary jockey Bill Shoemaker aboard, was galloping on the lead. Jockey Eddie Maple had Larida stalking her. They were setting a moderate pace, covering the first half-mile in 46 4/5 seconds, yet nobody was within eight lengths of them.

As they reached the final turn, Larida drew abreast of the leader, but couldn't get by; Shoemaker still had plenty of horse under him. But nobody had a stronger mount than 16-year-old Jack Kaenel, who had put Snow Plow into high gear.

"Early in the race, I had one horse beat," Kaenel said. "I had let her coast until the stretch when I got into her. I pulled her out into the middle of the track where the going was better." Snow Plow charged outside her rivals and drew away, covering the mile and one-sixteenth in 1:46 1/5.

The winner paid $19.60, $7.40 and $4.80. Ambassador of Luck returned $5.80 and $5 and Chilling Thought paid $3.80. It was a big day for Blusiewicz. He collected $126,501 for the victory, and announced after the race that he had leased the filly to Steve Peskoff, a Toledo, Ohio, investment banker, in a "six-figure deal."

And presumably, he must have cashed a little wager on Snow Plow, too.