A generation ago, horseplayers never used the term "track bias." Handicapping books never mentioned the notion that a racing strip might favor certain types of horses.

But the game has changed, and a modern-day bettor who cannot recognize and understand biases is doomed to the poorhouse. Track conditions have become a vital handicapping factor. Even in a championship event like today's $176,990 Selima Stakes at Pimlico, the speed, physical condition, experience and gameness of the fillies in the field may prove less important than the nature of the dirt they are running over.

Biases did not often exist in the by-gone era when tracks operated during a "racing season" in the temperate months of the year. But now that tracks run year-round, in all types of weather, it evidently has become much more difficult to keep racing surfaces uniform.

Whatever the reason, tracks that favor horses with certain post positions or certain running styles are now more the rule than the exception. At Saratoga this summer, I judged that there were nine days when the inside part of the track was clearly favorable, 10 days when it was clearly disadvantageous, and only five when the track was normal. Biases have abounded in Maryland this fall. At Laurel, horses who stayed on the rail had a big edge -- although they rarely stayed there, since jockeys were more preoccupied with avoiding the dangerous soft spots on the track.

When Laurel's racing strip practically fell apart, necessitating a shift of its meeting to Pimlico, bettors returned to a track that historically has favored horses with early speed and inside post positions -- especially at a mile and one-sixth. A horse cannot lose ground around both turns of a route race and win at Pimlico unless he is overwhelmingly superior.

Under such conditions, a handicapper will prosper if he does a minimal amount of handicapping. He should simply try to diagnose the horse who will get the lead along the rail. Even if that horse is not better than his rivals, the bias often will help him win. And if that horse happens to be the best one in the field anyway, he is a cinch.

There are a number of interesting speed-on-the-rail plays at Pimlico this afternoon. Blinkey's Bit in the second race and Bold Josh in the eighth seem to be at least equal in ability to their competition, and their inside posts should enable them to win.

In the sixth race, the superior horse happens to be the one who also has the bias in his favor. Hone lost a stakes race at Delaware by only two lengths his last start, and appears to possess an edge in class in this allowance race. He is a front-runner, and he has drawn the inside post at a mile and one-sixteenth. At Pimlico, that is the formula for a runaway.

The most interesting race on the card, however, is the Selima, the event which often determines the nation's champion 2-year-old filly. This year, however, that title already id decided.

Smart Angle clinched the championship by winning the Frizette Stakes at Belmont two weeks ago; it was her fifth stakes triumph in seven races this season. Her accomplishments dwarf those of the five fillies she faces today -- Street Ballet, Frozen Sails, Par Excellance, Gentle Ripple and Diorama. Of them, only Par Excellance has won a stake, and that was against nonentities in Canada.

Smart Angle has the speed, the consistance, the class, the seasoning, all the old textbook virtues. But she does not have the bias in her favor. Street Ballet does.

A speedster from trainer Bud Delp's stable, Street Ballet led all the way to win a sprint at Laurel by 14 lengths last week. Today she has drawn the No. 1 post position in the Selima, and if jockey Ron Franklin does not ride idiotically (which is always a possibility) she should have the rail all the way around the track.

In No. 2 post position is Frozen Sails, a noncontender, but a filly with early speed as well. Because Smart Angle breaks from the No. 4 post, she figures to be three horses wide in the run to the first turn, a significant disadvantage, and she figures to be outside Street Ballet all the way.

If the post positions were reversed, if Smart Angle had drawn the rail with Street Ballet outside of her, she would be a virtual cinch to win. But in the present alignment, Street Ballet has an excellent chance to pull an upset. Traditional-minded handicappers might laugh at the notion that seemingly insignificant post position assignments could determine the outcome of a race like the Selima, but people who think that way are the ones who go broke very quickly on biased race tracks.