It's called the London Season, that nonstop parade of social and sporting fixtures that runs from the Chelsea Flower Show in late May to the Cowes Week Yachting Festival in early August. In between there's racing at Ascot, test match cricket at Lord's, Wimbledon tennis, opera at Glyndebourne ... But as a timeless, undiluted English tableau, the Henley Royal Regatta wins by a full length.

Yes, there'll always be a Henley, and the glory of it is you don't have to be an old boy (read old grad) with a battered rowing cap to love it. You don't even have to be English. Henley (July 4 to 8 this year) is often portrayed as too stuffily parochial for foreign tastes, but in fact Americans are an important part of the show. Schoolboy and college crews from the United States have caused many a ripple down the years, and Yank followers are much in evidence on the banks of the Thames.

"They all look as though they had moved on at dawn from one of Jay Gatsby's parties," a columnist wrote in the Guardian on my last visit to Henley. "How is President Coolidge these days?"

Henley Royal Regatta, the world's oldest river regatta, was launched at Henley on Thames in 1839. Deep in the Oxfordshire countryside an hour's drive west of London, Henley is a pretty river town with timbered buildings, an elegant Georgian main street and an arched, 18th-century bridge; it's in the same storied neighborhood with Ascot, Eton and Windsor Castle; but the reason it's a rowing mecca is this: For one narrow mile and a little more, just below town, the impossibly sinuous river straightens out to form a perfect racing course.

Most of the mingling (viewing lawns, grandstands, car parks, boat tent) takes place in the waterside meadows just opposite Henley town, but the river's so narrow and Henley Bridge so convenient, people stream over and back all day. On Henley side they shop, rent punts and rowboats, crowd into pubs and cafes before traipsing back across the bridge to join the garden party disguised as an international sports fixture.

Somehow, down the years, the royal regatta has been kept a totally amateur event. Most of the 600,000 pounds spent to stage the races is covered by dues of members of the posh and exclusive Stewards' Enclosure, a sweep of green lawn and striped tents hard by the finish line. There are many ways to take in the 70-odd races each day on Henley Reach -- plop down on a towpath with a picnic lunch, rent a skiff or punt and watch from the water, buy a ticket (four or five pounds) to the public Regatta Enclosure -- but it's the Stewards' Enclosure every Henley-goer hankers after.

It's said to be one of the toughest tickets of the London Season; indeed, ads in the Times list phone numbers of touts who charge 50 pounds a day for the honor. But I found all it takes to open the gates of the Stewards' is a little Yankee ingenuity.

It was a stroke of beginner's luck that got me in the first day. Outside the Stewards' ticket booth I buttonholed a member who was about to go in, had him sign a voucher and then put down 9 pounds for a little pink badge (the color of which is changed each day). Next day, the man in the booth was less agreeable. I was about to consider other means of entry when two old boys dressed in Henley finery -- blue blazers, white flannel slacks, school ties, straw hats -- stepped up to turn in some unused tickets.

"Could I buy a ticket from you?" I asked the gents.

"I suppose so -- yes," said one, then added furtively: "Why don't we do this transaction somewhere else?"

We repaired to the Stewards' car park, full of old Rollses and new Range Rovers, and cut a deal: They'd give me a ticket, I'd buy them a drink inside and learn their view of Henley.

Henley is all about ritual, and one of the first things these old friends and oarsmen -- both in the publishing business -- do each morning is to stand under a tree at the white railing of the Bridge Bar, 20 feet from the water, and have a Pimms. Pimms and Henley, Henley and Pimms: Some 50,000 pints of the gin-based orange liquid, topped with slices of lemon, cucumber and mint, are sold at the regatta. And the Bridge is the bar of choice, ideal for race-viewing and people-watching.

Both men eschewed the traditional school blazer with its wild stripes or piping, and the well-worn cloth caps old boys haul out of their trunks once a year; they said both had gone out of style, at least in their circles.

Dress is important at Henley, but it's important not to look too dressed. The woman who goes beyond a long floral print dress and sensible heels is begging for that rare English reaction: the long stare. On the other hand, Stewards' rules bar bared knees, and each day a few mini-skirted violators are summarily bounced -- some to return, with classic British pluck, with a sweater hiding the exposed flesh. Peter Koni, regatta director, bristles when he sees the coverage accorded the sartorial offenders. "It's all a ploy to get one's photo in the papers," he said. "It reminds one of Lord's {cricket} or Wimbledon -- God forbid we should sink to that."

Some say nobody goes to Henley to watch the rowing, but this is belied by the crowds that fill the Stewards' grandstand and rise to their feet at the close of a close race, and by the sports chat one hears in the enclosure. Move about the clipped lawns, banks of hydrangeas and rustling maples and you also hear talk of school, marriage, babies, divorce -- but never business. Regatta rules hold that business clients must be wined and dined, Pimmed and strawberried in the striped corporate tents downriver, which blare with Dixieland well into the lingering dusk.

One of the ageless ironies of Henley -- of all rowing -- is that it's hard to follow a race from start to finish. Henley Reach, the only straight stretch of the Thames, is a longish 1 and 5/16th miles, just wide enough for two boats to thrash it out. All one can see from a given point is a pair of sculls -- singles, doubles, fours or eights -- dashing by at 20 miles per hour.

Maybe the best view is from the umpire's launch -- another old Henley nut that can be cracked with pluck and luck. The handsome wooden inboard runs upriver to the starting line of each race, waves the boats into action, then putters back in their wake. Each launch takes a dozen guests, mostly friends and family of the rowers, but one may chat up the umpire and catch a ride.

One institution even an insider has trouble denting is the legendary Leander Club, England's most prestigious rowing club. You can spot Leander men by their pink -- sorry, cerise -- trim: cerise tie, cerise cap, cerise socks. The old brick clubhouse doesn't look like much and it's a distance from the finish line ("Very badly placed," sniffed a nonmember I met), but rowers consider it a towering honor to wear the Leander colors.

"I would have murdered to get in," said a fiftyish London friend of mine, a onetime Oxford oarsman. "I was sick at a critical time, missed out and was absolutely distraught."

If you're looking for the American presence, it's never hard to spot. The young men in those shocking orange blazers row for Syracuse University, the Princetons are in beige jackets with orange piping. But perhaps the most arresting sight of all is the outrageous purple worn by the University of London lads.

Late on a sultry Thames Valley afternoon, Henley looks more like a drowsy Edwardian tableau than ever. On the Stewards' lawn, faded perfume mingles with the smell of hops from the red-brick Henley brewery across the river. Ties are loosened, heels are kicked off beneath cafe tables and cloth chairs, as the Pimms and champagne, lobster, crab and salmon lunches complete the day's ambush. Over it all float the measured tones, never intrusive, of the P.A. announcer: "Salisbury lead by one and a half lengths, stroking 36 ... "

I say, did you see Lloyd George today?

David Butwin is a writer in Leonia, N.J.

Unless you are bent on cracking the Stewards' Enclosure (not an impossible task), the Henley Royal Regatta (July 4 to 8 this year) makes for a convenient and pleasant outing from London. It's an hour's drive via the M4 motorway from central London or an easy run with British Rail from Paddington Station. There's a lawn-party atmosphere aboard the train, with people in rowing caps and striped blazers carrying wicker lunch hampers.

Another way to do Henley right is to rent a car, preferably something sporty (Morgan? Rolls?), and idle away lunch hour and Pimms breaks in tailgate fashion on the car-park lawns. You can stay overnight in the area; there are small waterside hotels in Henley and inns, country hotels and bed-and-breakfast houses scattered through the Oxfordshire countryside, many with Thameside settings: swans and ducks and passing houseboats beneath your window.

If you want to spend $260 a day, the Keith Prowse tour operator in New York can arrange a full day at Henley that includes admission to the Prowse hospitality tent, unlimited bar, four-course lunch and Dixieland music. Prowse also can set up tickets and packages for Wimbledon and other summer fixtures. During the Wednesday-Sunday Henley run, for example, visitors can also take in the second week of Wimbledon (June 25-July 8 overall), the Cornhill Insurance Test Match (cricket) between England and New Zealand at Edgbaston (July 5-10) and Glorious Goodwood at Goodwood Race Course near Chichester in West Sussex (July 31-Aug. 4). INFORMATION: For more information on the Henley Royal Regatta, contact the British Tourist Authority, 40 W. 57th St., New York, N.Y. 10017, (212) 581-4700. For information on the Prowse packages, contact the Keith Prowse agency, 234 W. 44th St., Suite 902, New York, N.Y. 10036, (212) 398-1430 or 1-800-669-8687.

-- David Butwin