The best thoroughbred handicapper I know started his career as a kid by perching atop a billboard, watching the harness races at Yonkers through binoculars and flashing the results to the bookmaker who was his employer.

His background was not atypical. Most astute horseplayers of my acquaintance got their start by betting on trotters and pacers. It took me years to realize that this was no mere coincidence.

Harness racing can be a great educational experience because it makes obvious the importance of certain factors that are much more subtle in the thoroughbred game. Bettors learn quickly that the way races develop, in terms of pace, strategy and ground lost, usually determines their outcome. So when they make the transition to thoroughbred racing, they are sensitized to the importance of these factors and they perceive things that a lifelong thoroughbred handicapper may not.

A neophyte at a harness track should learn in an hour or two that a horse's chances will be compromised when he has to make his move very wide around the turn. I spent a decade or two betting thoroughbreds before the same thing dawned on me.

In my misspent youth I learned little about harness racing, which I now realize was a serious oversight. So I spent a recent evening at Freestate Raceway in the company of an expert, attemping to acquire at least a kindergarten-level understanding of the sport.

Bill is a full-time professional harness bettor who conducts most of his activity at Rosecroft and Freestate. He employs some sophisticated analytical methods, but knowing how to watch races is the crucial skill in his trade.

The obvious, overriding factor in the game is the ground that horses lose by going wide on the turns. "On a half-mile track," Bill said, "a horse who is parked for the entire mile has to go an extra 64 yards. Being parked on one turn can cost him four lengths or more.

The second crucial factor is wind resistance: some horses will be shielded from the wind -- "get cover" -- for most of the race, while others must run headlong into it.

"It's hard to quantify its effect," Bill said, "but don't ever underestimate the effect of air. A lot of times when people say a horse has no heart they really mean he can't take air."

A third major factor is pace. When the leaders have gone a slow half-mile, it's difficult for anything but a very superior horse to spot them several lengths and overhaul them when they are still strong.

To watch races intelligently, a handicapper must judge which horses are helped and hurt by these factors. To find optimal future bets, Bill said, "What you look for is a trip such that there's no way the horse can win."

For example: In the second race at Freestate on Wednesday, a filly named See Me pulled out after the leaders had gone a slow second quarter. She was "first over" -- the horse who makes her move without cover. Because the horses in the lead were still strong, she couldn't surge by them, and wound up parked three-wide all the way around the final turn. That is the kind of trip with which few harness horses can win, and any good handicapper will note the circumstances for future reference.

Conversely, Bill said, he will remember horses who have perfect trips, who encounter circumstances so favorable they have to run well, and look to bet against them when they run again. "The most obvious type is the horse who sits the perfect two-hole trip."

A horse runs second all the way, with the leader providing him cover, then swings past him in the stretch, while all the other contenders are forced to lose ground on the turn.

Trips are so important in harness racing that they can easily obliterate a 10-length difference in ability between two horses. In Wednesday night's fifth race at Freestate, Chipmans B T scored a narrow victory over Big Brite and Glenwood Topper, but the margins at the finish gave no clues to their relative ability.

Chipmans B T had moved three-wide all the way around the turn to gain the lead. Glenwood Topper had been blocked on the turn, then had to angle out and alter his course to get racing room in the stretch. While they were encountering their difficulties, Big Brite had a perfect trip, running second with cover almost all the way. "Big Brite was anywhere from six to 10 lengths inferior to the other two horses," Bill said. That is information on which he will capitalize if this group of horses meets again.

Such perceptions are elementary to the regulars at Freestate, or any other harness track. They know that it is an exercise in futility to bet harness races without having observed horses' trips in their previous starts, or without trying to judge what kinds of trips they are likely to have tonight. For thoroughbred players that is a lesson worth learning.