HALLANDALE, FLA., MARCH 4 -- It would be a reasonable proposition to bet that the winner of the 1988 Kentucky Derby is a colt running at Gulfstream Park Saturday.

The $500,000 Florida Derby has drawn an exceptionally strong field, filled with the leading horses of this generation. Since most of the prominent 3-year-olds in California have discredited themselves, and no stars have appeared in Arkansas or New York, this is almost surely going to be a definitive prep race for the Triple Crown series.

There are at least five solid contenders in the 10-horse field -- Forty Niner, Notebook, Cherokee Colony, Sorry About That and Ruhlmann -- and they may be so evenly matched that the 1 1/8-mile event will come to a rousing but inconclusive finish. But if one of them can manage to win decisively, he instantly will be recognized as the leader of his age group.

Forty Niner holds that distinction temporarily, and he will be the Florida Derby favorite as a result. But the support for him is based on his laurels as the 2-year-old champion of last season, as well as respect for his legendary trainer Woody Stephens, rather than on his performances here this winter.

In the Fountain of Youth Stakes, the main prep for the Florida Derby, Forty Niner and Notebook engaged in a head-and-head duel all the way around the track, with Forty Niner eking out the photo-finish decision. Notebook was parked on the outside all the way; he was probably the better horse that day. Moreover, that the two colts covered the final sixteenth of a mile in a slow seven seconds raised doubts about their ability to go much farther.

Stephens himself once harbored such doubts about Forty Niner's stamina, but he has gained confidence in his colt as the winter has progressed. He is clearly delighted with the way Forty Niner has trained for this race. "What he can't do now," the Hall-of-Fame horseman said, "he just can't do, period."

Earlier in the year, the Flamingo Stakes at Hialeah had produced another thrilling 3-year-old battle, with Cherokee Colony rallying strongly to defeat Sorry About That. Cherokee Colony evoked memories of his sire, Kentucky Derby winner Pleasant Colony, and because he looks like one of the few solid stretch runners of his generation he got heavy support in Las Vegas' future-book betting on the Derby.

Johnny Campo has done nothing to quell such enthusiasm. "He's a better made horse than his father," the voluble trainer said. "He's got better action than his father. And he wants to go long -- a mile and an eighth, a mile and a quarter."

Even though Cherokee Colony has a genuinely strong stretch kick, the groundswell for him may be ill-founded. His winning time in the Flamingo was mediocre (much worse than that of the Forty Niner-Notebook duel), and he may not have been as good that day as Sorry About That, who had a very rough trip. "In all his races," trainer Sonny Hine lamented, "he's been stopped once or twice." Even with his bad luck, Sorry About That has won three of four lifetime starts and deserves more attention and respect than he has been getting here this week.

The mystery horse in the Florida Derby lineup is the California invader Ruhlmann. He had won only once of his first six career starts before trainer Bobby Frankel equipped him with blinkers and added jockey Pat Day, and the colt responded with a smashing six-length win in sensational time. The meaning of this performance was ambiguous, but Ruhlmann has trained so spectacularly since coming to Gulfstream, and clockers have heaped him with such superlatives, that he is expected to be second choice in the wagering.

The others in the lineup are Brian's Time, Frosty The Snowman, Buoy, Evening Kris and Twice Too Many. All except the latter are considered at least marginal contenders.

Because the field seems so evenly matched, riding tactics and racing luck could easily determine the outcome of the Florida Derby. Most of the contenders -- especially Forty Niner, Notebook and Ruhlmann -- have great natural speed, but none of the jockeys wants to get into a hard fight for the early lead. Almost everybody involved in the race wants to see his horse relax and settle into a good striking position, just off the early leaders. The horse who manages to do it could be the winner.