In 1850, Admiral John Francis Rous formulated racing's first scale of weights, which dictated the concessions that older horses should give to younger horses in order to equalize everybody's chances. It has evolved slightly over the years, and today the Jockey Club Scale of Weights has the authority of holy writ.

In 1965, John D. Schapiro formulated the Schapiro Scale of Weights, which decreed what horses of different ages should carry in the Washington, D.C. International. It was his track and his race, and he could do whatever he wanted, but Schapiro's tinkering had a significant impact on the subsequent history of the Laurel Race Course classic. Weight may be a dominant factor again in Saturday's 30th running of the International.

The Jockey Club Scale of Weights calls for 3-year-olds to get a four-pound concession from their elders in a 1 1/2-mile race run in November. The International was run under these conditions during the first 13 years of its history, and older horses won 11 times. There weren't many top 3-year-olds in the International during this period; in fact, no 3-year-old was favored in those 13 races. But Schapiro concluded that the time-tested scale of weights gave an unfair advantage to older horses, and so he amended it.

Starting in 1965, 3-year-olds would carry 120 pounds; older horses would carry 127. (All females get a three-pound concession.) Even those of us who tend to minimize the importance of weight in handicapping have to concede that this change had a dramatic effect. Three-year-olds have won 11 of the last 16 runnings of the International, and even that statistic doesn't begin to tell how dominant they have been. In three of the years when older horses won, there wasn't a single well-regarded 3-year-old in the race.

So in a field like this year's, where no horse seems to possess clearly superior ability, the scale of weights should give the 3-year-olds the advantage. April Run, Open Call and (possibly) Beldale Flutter are the horses most likely to succeed Saturday.

The filly April Run finished a close third in Europe's most prestigious race, the Prix de l'Arc de Triomphe, then came to New York and won the $300,000 Turf Classic by a narrow margin over the 5-year-old Galaxy Libra.

On paper, the two horses are hard to separate. But when I asked three expert handicappers in New York what they thought of the race, all concurred that April Run was clearly superior. Accustomed to the sweeping European courses, she had trouble negotiating the sharp turns at Aqueduct, but she still won with authority and was eased up in the final yards. Galaxy Libra saved ground most of the way and yet never seriously threatened April Run, even though the final margin was only three-quarters of a length.

April Run's performance in the Turf Classic didn't make her look like a super filly. To beat Galaxy Libra was no great feat; he had only a three-for-nine record in California this year while getting weight concessions in most of those races. If there were a truly superior horse in the International field, he could whip April Run.

And, indeed, there might be such a horse: Open Call. The 3-year-old has run on the grass six times. He lost once because of an uncharacteristically terrible ride by jockey Jorge Velasquez, but won all the other five with total authority. In his last start, he ran away with the rich Rothmans International Stakes in Canada. But the rivals behind him that day were not a distinguished group; in fact, Open Call has not yet beaten a field that proves he is in April Run's class.

If Open Call is somewhat enigmatic, the English 3-year-old Beldale Flutter has form that seems inscrutable to an American horseplayer. Last season, he scored a victory over Shergar, who was later being acclaimed as a true super horse. This year, he beat a top field in the prestigious Benson and Hedges Gold Cup. Then, in the 24-horse Prix de l'Arc de Triomphe, he finished 23rd. Such mysteries make the International such a difficult race to bet.

Still, the challenge is irresistible. Because of the lessons of history, I plan to throw out all the older horses in the race -- Galaxy Libra, Providential II, Match the Hatch, Cairn Rouge and Siapa Rajah III. The 3-year-olds Rainbow Connection and Johnny Dance seem a bit overmatched. Unable to choose among the others, I will box April Run, Open Call and Beldale Flutter in the exacta, and hope that the 3-year-olds' dominance in the International continues for yet another year.