The major fall stakes races at Belmont Park usually determine the country's best racehorse, but this year the contenders have taken turns beating each other.

Track Barron won the Woodward Stakes. Chief's Crown took the Marlboro Cup. Vanlandingham won the Jockey Club Gold Cup. So, when the same cast of characters is assembled again for the $3 million Breeders' Cup Classic Saturday at Aqueduct, it may be futile to ask who the best horse is. The more appropriate question may be: whose turn is it?

And the answer may be: It's Gate Dancer's turn. The runner-up in the last two major stakes races, he is long overdue to shed his bridesmaid role and win a big one.

The Classic seems likely to be won by a horse with a stretch-running style like Gate Dancer's, because the two principal speed horses in the field, Track Barron and Vanlandingham, are likely to bring about each other's destruction.

Track Barron never has won at 1 1/4 miles and never has given an indication that he can go that far, but his speed has brought about Vanlandingham's demise before. In races in which he hasn't had to face Track Barron, Vanlandingham is four for four this year, leading all the way in each. When he has had to cope with Track Barron, he is zero for three.

The last time these two hooked up with each other, in the 1 1/4-mile Marlboro Cup, Chief's Crown rallied to beat Gate Dancer in a photo finish. Chief's Crown ran the race of his life that day -- it was the only time he ever has beaten a high-class field -- whereas Gate Dancer is capable of better.

If this sounds like a tepid opinion, it is. The contenders in the Classic are so evenly matched that it's difficult for a handicapper to hold an ironclad opinion on the race. Other events on Saturday's program are much easier to analyze:

Juvenile -- On the basis of his nine-length victory in the Champagne Stakes at Belmont, Mogambo will be a heavy favorite to beat 13 other 2-year-old colts. But that performance wasn't as impressive as it may have looked. Mogambo's time of 1:37 1/5 for the mile was mediocre, and he doesn't merit a wager at a short price. I'd rather take my chances with the Maryland colt, Papal Power, who won Saratoga's Hopeful Stakes, finished second in the recent Laurel Futurity and will probably be 10 to 1.

Juvenile Fillies -- Trainer Wayne Lukas has a virtual lock on this event, with a three-horse entry of Family Style, Arewehavingfunyet and Twilight Ridge. This might have been an interesting betting race if Lukas didn't train them all. Twilight Ridge hasn't won major stakes (her stablemates have), but she is the most talented member of the trio.

Sprint -- This six-furlong race may be the most interesting and competitive event on the whole Breeders' Cup card. The California colt Precisionist is the most talented member of the field, but he hasn't raced since mid-June. Fighting Fit gave the most brilliant performance of any sprinter in the United States this year when he won a stakes race at Aqueduct last winter. He returned to competition with a sharp second behind Mt. Livermore in the Fall Highweight Handicap last month. But Mt. Livermore may have a slim edge Saturday. Oddly, he is the only contender in the field with blazing early speed, and he may be able to lead this race all the way.

Mile -- The European cognoscenti assure us that the French 4-year-old Rousillon and the English 3-year-old Shadeed are the best milers in the world. These are the same cognoscenti who assured us last year that Lear Fan couldn't lose the Mile (he did) and that Lashkari had no chance in the Breeders' Cup Turf (he won at 53 to 1). But Rousillon's credentials do look especially impressive. He has won all three of his 1985 starts, two of them Grade I stakes, over three different tracks. He and Shadeed should be able to beat the good American colt Cozzene and the rest of the home forces.

Distaff -- It's another victory for Wayne Lukas. Lady's Secret, who has won eight races in a row, is the clearest standout of the whole day, and if she falters at the 1 1/4-mile distance, her stablemate Life's Magic could save the day.

Turf -- This much is certain: a European horse will win this $2 million event. The American forces look totally outclassed. The filly Pebbles will be the favorite, but the French colt Shernazar could pull an upset. Shernazar won his first three starts this year and defeated English Derby winner Slip Anchor, but encountered terrible racing luck and finished 12th in the Prix de l'Arc de Triomphe.

Still, after Lashkari's implausible victory last year, any handicapper should approach this race with trepidation. And that caution should be carried over into the Breeders' Cup Classic.