When a filly named Believed Sunny appeared in a weak maiden race at Belmont Park last week, most handicappers would have paid little attention to her. She had made only two previous starts, both in Kentucky last fall, and the best she had ever done was a 16-length defeat.

Through most of the wagering, Believed Sunny's odds hovered around 8 to 1. As post time approached, the price dipped to 6 to 1. As the field neared the gate, she dropped to 9 to 2, and any bettor at the track had to answer a crucial question: Was this "smart money"? Was it a meaningful sign that the filly was better than her record suggested? Or was it just an enticement for a sucker to bet on a bad horse?

The answer came emphatically, when Believed Sunny blew past her rivals and drew away to a 10-length victory. The result was a confirmation of a fact every serious bettor recognizes: The tote board sometimes can be one of the most critical factors in the handicapping process.

When neophytes start watching the tote board, and see "hot horses" like Believed Sunny win, they assume some sinister, all-knowing handful of insiders is controlling the game. But odds are set in a much more complex fashion -- with a mixture of the opinions of owners and backstretch employes, good handicappers, as well as the public at large (whose intelligence should not be underestimated). One of the most amazing demonstrations of smart money I have ever seen came not in any maiden race but in the Kentucky Derby and Preakness of 1986. Snow Chief was widely expected to be an overwhelming choice in the Derby, but he got unexpectedly tepid support in the wagering. Yet, after Snow Chief was trounced by 20 lengths, and most expert commentators ignored him before the Preakness, the Pimlico bettors made him an astonishingly short price, 5 to 2, and he won easy. No larceny or inside information was involved, but the tote board was right again.

When bettors become too conscious of betting action and attempt to follow the "smart money" slavishly, they are apt to go astray more often than not, because the tote board's messages can often be misleading and costly. Having paid considerable tuition over the years, I think I understand board-watching well enough to offer a few pointers.

The cardinal rule: A bettor shouldn't let the tote board make his handicapping decisions for him. He should let betting action sway him only in cases where a horse's form is unexposed, where insiders might know more than a student of the Daily Racing Form could. If I am comparing horses who ran good races a week ago, I don't care what the board says; I'll trust my judgment. But I'll pay special attention to betting action when I am trying to deal with first-time starters, horses who have been laid off, lightly raced maidens or horses with a recent bad race that might have been due to larceny or other factors I don't know about.

The key to detecting genuine "smart money" is to spot betting action on horses the general public would not ordinarily play. It is not enough to compare the horse's actual odds to the morning line, because the morning lines published in most track programs (including Maryland's) are lousy. One must understand that the public always likes to play horses dropping in class; horses whose last race is a recent, sharp effort; horses being ridden by a hot jockey. Horses with obvious credentials, in other words.

When Bernie Bond -- an ace trainer of first-time starters -- saddled a firster named Empress Tigere at Pimlico last week, and the filly showed a five-furlong workout in 1:00 1/5, it meant little that she was bet down to 2-to-1 favoritism. The public would almost always support a horse like that. Empress Tigere finished third. But when Marvin Moncrief -- a trainer not well known in New York -- sent King's Nest to Belmont Wednesday, and the first-time starter showed unimpressive half-mile works in :49 and :50, the tote board spoke meaningfully when King's Nest was 3 to 1. He won by five.

What form does genuine betting action take? It's hard to generalize. Money that shows early in the wagering can be deceptive because the betting pools are so small; a $200 bet can affect the early odds at Maryland tracks, and I would not pay much attention to it unless the horse is getting support in the exacta pool as well as the win pool. Most bettors are used to looking for sharp drops in horses' odds just before post time. That often is important, but I believe the best type action is steady support for an improbable horse throughout the wagering, possibly followed by one final big punch near post time -- the type that Believed Sunny took.

One of the most reliable and, at the same time, potentially deceptive messages that the tote board can send is with negative betting action. When a horse appears certain to get solid support from the general public, but instead is "dead on the board," he usually won't win. It is best to heed this message in cases where the horse's current form is hidden. In the third race at Freestate on Thursday, the undisputed class of the field was a filly named Allagashtoni, but she hadn't raced for two months. She figured to take some public money, but when she went off at 8 to 1, the board's message was obviously negative, and Allagashtoni finished next to last.

If a horse with solid, recent handicapping credentials is "dead on the board," the case is trickier. When an obvious standout who figures to be an odds-on favorite is 3 to 1, and the unwary are saying, "This is a gift," it may pay to be wary. But unless a bettor knows exactly what he is doing under such conditions, he can make some demoralizing mistakes.

My pal Jerry went to Pimlico recently to bet a King Leatherbury-trained colt named Prince Rio, who had given a terrific performance winning his career debut on the grass. Jerry was hoping to get odds of 5 to 2, but when Prince Rio was 6 to 1 through most of the betting, Jerry said, "Leatherbury has a betting stable, and he has to know how good this horse is. Something's wrong."

Jerry switched his bet to his second choice, Ringing. When Prince Rio romped home and paid $12.40, and the exacta with Ringing returned $101.20, Jerry had to take a sabbatical from the track to restore his mental health.

Watching the tote board has many rewards, but it also presents its share of pitfalls.