n an era when thoroughbreds commonly do all of their serious racing at the age of 3 and are quickly retired to stud, the gelding Winter's Tale is demonstrating what can happen when a racehorse is permitted to develop slowly and reach maturity.

He has had a checkered career until now, but at the age of 6 Winter's Tale seems ready to deliver some of the best (and most lucrative) performances of his career. He is the cofavorite in Saturday's $227,500 Woodward Stakes, the first leg of Belmont Park's fall championship series that offers a $1 million bonus to any horse winning all three of its races.

Winter's Tale hasn't often had the chance to run in such important races when he was healthy. "He's had a lot of problems," trainer Mack Miller said. "When he was 2, he had trouble with his ankles and didn't race at all. When he was 3, he developed a sinus condition and they had to go into his upper sinuses with a surgical drill. In the fall of his 4-year-old season, he had a chip in his knee. And last fall, he hurt his back and he had to spend six months on the farm."

In the midst of all these travails, Winter's Tale showed what a good horse he can be. During a three-month period in 1980, he won four major stakes in sensational fashion (including the Marlboro Cup, by 4 1/2 lengths) and earned more than $400,000. Now he seems to be in the same kind of form.

He set a track record in an allowance race at Saratoga two weeks ago and, in the race before that, lost by 1 1/2 lengths to Silver Buck in the Whitney Stakes. On that day, Winter's Tale had been assigned to carry 119 pounds and Silver Buck 115. "I thought that was ridiculous," Miller said, and most of the racing world agreed with him.

On Saturday, the tables are turned. Under the complex allowance conditions of the Woodward, Silver Buck will carry 126 pounds and Winter's Tale 119.

Just about every handicapper has a pet theory or formula with which to assess the affect of such a change in weights. In his "Complete Guide to Thoroughbred Racing," Tom Ainslie decrees: "Two extra pounds of weight slow a horse by one fifth of a second at a mile and one eighth." With that 11-pound shift after his 1 1/2-length loss in the Whitney, Winter's Tale is supposed to win by four lengths under the Ainslie formula.

In fact, it's impossible to generalize about the importance of weight because different horses are affected by it differently. Silver Buck has never carried high weight before. But Winter's Tale has shown that a few pounds can be very important to him. Miller concedes, "I think he might be suspect as a weight carrier." The break in the weights probably gives him the edge over Silver Buck and the rest of a 10-horse field that includes It's The One and Wavering Monarch.

While the intricacies of handicapping the Woodward may appeal to hardcore fans, this race is not the exciting, championship event that it was supposed to be. The $1 million bonus that goes to a winner of the Woodward, the Marlboro Cup and the Jockey Club Gold Cup was supposed to attract all the best horses in the country.

But that lofty sum is still paltry when compared to the money in the breeding business, and so owners don't care about winning purses any more. Instead, they want their horses to compile a record that will look good when they go to stud.

Timely Writer is passing the Woodward to run against other 3-year-olds in the Jerome Handicap here on Monday. Conquistador Cielo, who should have been the star of these fall races, has already been retired -- rather than risk confrontations with Silver Buck and Winter's Tale that could have sullied his record. Fortunately, 6-year-old geldings don't have to worry about safeguarding their reputations for their stud careers. Perrault Entered

Perrault, the Budweiser Million champion, will run in the $250,000 Washington, D.C. International at Laurel Race Course.

A track spokesman said yesterday that the horse's owners, Serge Fradkoff and Baron Thierre von Zuylen, had sent wires of acceptance for the Nov. 6 race. Perrault is at Belmont Park preparing for the $400,000-added Marlboro Cup Sept. 18.