When I return to Washington from a Kentucky Derby, friends inevitably ask me: What was it really like? They sense, correctly, that the Derby is an event that cannot be captured within the limits of a 21-inch screen.

Unlike the Super Bowl and the World Series, whose essence is the game itself, the mystique of the Derby depends on the glamor, hoopla, the social activities that surround it. But racing fans who watch Saturday's battle between Spectacular Bid and Flying Paster on Television should not feel terribly shortchanged. While the Derby itself may be the most exciting two minutes in sports, Derby Week can be tiresome, tawdry and maddening.

The worst thing about the Derby is that it takes place in Kentucky. It culminates a week of racing that can fill even the most diehard horseplayer with distaste for the sport.

While other states make occasional gestures of concern for the betting public, Kentucky's racing is conducted by and for the benefit of its breeding establishment. It strikes nobody here as odd that the chairman of the racing commission should be one of the most powerful breeders in the state, which is a bit like having the president of Exxon double as the nation's energy czar.

I had to watch only one race here this spring to know that things hadn't changed since my last visit to the bluegrass country. In the first race at Keeneland on Thursday, a horse who had lost his last start by 41 lengths and had been laid off for six weeks with no published workouts was bet down to 5 to 2. He won in a gallop.

And that was a mild from reversal compared to the outrages that will be perpetrated as Derby Day approaches. Every conniving trainer saves his best chicanery for the days when the out-of-town lambs are at Churchill Downs for the annual slaughter.

If horsemen performed such shenanigans in other racing areas, indignant horseplayers woule be on the verge of burning down the grandstand. But trainers can play games here, not only because they have the tacit consent of racing officials but also because most bettors here are not smart enough to know they're being hoodwinked.

This is quite the opposite of most people's notions of what the Derby crowd is like. Before I had ever come to Louisville, I envisioned Derby Week as it was depicted in the movie, "The Hustler," as a fascinating confluence of horseplayers and gamblers and hustlers and action guys of every description.

In fact, it is not. The coveted box seats at Churchill Downs are heavily controlled by corporations which use the Derby as an excuse for business entertaining. The other large segment of the Derby crowd is college students who converge on the infield for a giant beer blast.

So Louisville bears little resemblance to a Saratoga, where you can walk into almost any bar and hear lively and intelligent talk about horses. Here you walk into a bar and you'll see either some inebriated oil company execs or some inebriated U of K undergrads.

It does help considerably to be inebriated to get through a week in Louisville. From the viewpoint of any urbane visitor, the city is a wasteland, its downtown decaying, devoid of good restaurants, good nightlife or any other perceptible virtues. If it weren't for the Derby, Louisville could sink into the Ohio River without the world noticing or caring.

Paradoxically, it is the very dreariness of Louisville that has helped give the Derby its unique character. The Preakness and the Belmont and most other great American races occur in cosmopolitan areas whose inhabitants have other things to do besides go crazy over a horse race. As hard as Pimlico tries to create a "Preakness Festival" comparable to Derby Week, the effort is doomed to failure because Baltimore is too sophisticated.

Louisville embraces the Derby as no other city (except, possibly, Indianapolis) embraces a sporting event. Youngsters grow up steeped in Derby lore. Top-40 stations play tapes of the calls of Derbys of the past. Every rock and roll band in every sleazy bar can move its audience to tears by playing "My Old Kentucky Home."

A visitor here scarcely can avoid being infected by the city's mania for the Derby. He will come to share the local belief that every Derby, no matter how weak the field or how uneventful the race, will occupy its own special niche in history. The buildup the city gives to each Derby confers on it a sense of excitement that dwarfs legitimate championship races elsewhere.

Even if a cynical visitor attempts to avoid being caught up in all the hoopla, he will find that post time for the Derby is perhaps the most electric moment in American sports-one that almost makes up for having spent the previous week in Louisville awaiting it.