The most astonishing auction in the history of the Saratoga Yearling Sales started innocently enough last week.

Somebody offered $50,000 for a 1-year-old colt by Exclusive Native out of La Jalouse, and the price quickly escalated to $500,000. That was approximately the figure the seller had been expecting and that the animal was worth on today's market. His pedigree did not merit much more.

But as the auctioneer asked if there were any further bids, two men were evidently taking a deep breath and steeling their resolve. At first there had been three bidders for the colt; one of them, Thomas Mellon Evans, had dropped out. Two remained: Louis Wolfson, the financier who had owned Affirmed, and Aaron U. Jones, a wealthy Oregon lumberman.

In a matter of a few seconds, the bidding went wind: Six! Seven! Eight! Nine! As ordinary horse buyers bid thousands, Wolfson and Jones were countering each other with bids in units of $100,000. When they reached $1.2 million, auctioneer Laddie Dance was about to lower his hammer, when Leslie Combs, the seller of the colt, hollered, "Take your time!"

The brief respite was all Wolfson and Jones needed to give them further strength. They kept on bidding, and when the gavel finally fell, Wolfson had spent $1.6 million for the second most expensive thoroughbred yearling in history.

In this era of astronomical prices for horseflesh, the sum itself was not incredible. But that sum for this colt was. Exclusive Native, of course, is the nation's leading sire, the daddy of Affirmed and Genuine Risk. But LaJalouse was not a proved broodmare. In the parlance of the breeding world, this yearling did not have a "sire pedigree," meaning that his genes would have little future value at stud no matter what he did on the track. He was, by any rational standards, a bad investment.

Why would a sagacious financier do anything so rash?

That quetion has been the talk of the town since Friday night, and the most popular explanation is a conspiratorial one.

For years, people have suspected Spendthrift Farm, which sold the yearling, of setting up record sales, with the buyer and seller secretly working hand in hand so they can enhance the prestige of a stallion.

The relationships between the principals in Friday night's auction were so incestuous that such a theory seemed very plausible. Wolfson owned Exclusive Native, and retained several shares in him when he went to stud at Spendthrift Farm. Wolfson and Jones both campaign their horses under the care of the same trainer, Laz Barrera.

But there are othr insiders who believe that their sharing of Barrera's services has created some friction between them, and they got carried away in the auction because they wanted to beat each other so badly.

This happens often in the high-pressure atmosphere of the yearling sales. Charles Engelhard, the late "platinum king," used to get involved in frequent duels that proved he could outspend any rich man who challenged him.

Elizabeth Arden and Isabel Dodge Sloane engaged in many fierce bidding duels. Arden was considerably richer, frequent purchaser of high-priced horses, and once when an unfashionable animal came into the ring she turned to Sloane and said, "Here's one that will do for you, Isabel." From that time on, Sloane was regulrly running up the prices of Arden's purchases.

All that is needed to make a record price are two bidders with a like-minded attitude. Wolfson had come to Saratoga with the expectation of buying the Executive Native-La Jalouse colt. In fact, Spendthrift had sold him here (instead of Keeneland, where it usually markets its top yearlings) precisely because Wolfson would be attending this sale in person and would be able to see the colt's exemplary conformation.

When Jones entered the bidding, Wolfson wasn't about to change his mind. It might seem illogical that a man would pay such a premium for one colt when better animals were available for cheaper prices, but man is not necessarily a logical creature.

"Why," asked John Finney, president of the company that conducts the sales, "with all the women in the world are there barroom fights? Because men take the attitude: 'That's my girl; leave her alone.' So two wealthy men can take the attitude, 'That's my colt, Leave him alone.'"

Wolfson, of course, still could wind up a winner for his temporary folly. Top thoroughbreds can pay their owners enormous dividends. Exclusive Native's most illustrious son, Affirmed, earned $2 million for Wolfson and was syndicated for $14 million. "The history of this business over the last 20 years," Finney said, "is such that yesterday's fool is tomorrow's genius."

It hardly matters that the odds are stacked against Wolfson, that this animal is unlikely to earn him anything approaching a $1.6 million return. "A colt like this," Finney said, "is not an article of commerce. He is an article of passion."