As a Rolls Royce pulled up, and a regally dressed couple emerged to swoosh through the entrance of the Stewards' Enclosure, Neil Hatton nodded to the people inside. "A lot of upper-class people get very drunk; it's really fun to see them smashed," he grinned. "Hardly anyone goes to see the rowing."

Then, he adjusted his tie, flashed his badge to the security guard and disappeared into the crowd celebrating Britain's rowing extravaganza--and four-day party--the Henley Royal Regatta.

Among the outsiders are the American oarsmen competing with the 260 crews and scullers in the 1983 regatta, and although they are made welcome, they hardly have time to frequent the Stewards' Enclosure, an exclusive private club on the banks of the Thames.

In opening day action, Georgetown University's four-man crew led Nottingham University for the first half-mile, but fell behind and lost by 1 1/2 lengths over the 1-mile 550-yard course.

The 144-year-old regatta runs two-boat, single-elimination heats, so Georgetown is now out of the competition for the Challenge Cup.

The club is the center of the social scene, and young and old socialites frantically try to wrangle guest tickets from members. Membership is by election only and usually limited to rowers and those in rowing circles.

"I was overwhelmed by the commotion," said Jack Kinch, a New Yorker rowing on the Georgetown Four. "Everything's so beautiful, so proper."

His fellow oarsman Mike Rollings added, "There's no comparison with American regattas. This is in a totally different ballpark We've just been wide-eyed the last few days. They row differently, talk differently, dress differently."

The style is quintessentially upper-class British. Men are not admitted to the Stewards' Enclosure without jacket and tie; women must wear dresses or skirts. Hats and gloves are optional for women, but one said, "I would feel naked without them."

Henley, normally a quiet town divided by the Thames 25 miles west of London, comes alive for the regatta. Pubs stay open almost all day, and motorboats crowd the half of the river not used for the race.

Those who rowed in the regatta when they were at Eton or Oxford come back to clap each other on the back and eat lunch into the most exclusive club, the Leander, where the elite wear bright pink ties.

After eating salmon, they walk, boater hats in hand, 100 yards past the boat houses to the Stewards' Enclosure for strawberries and cream and an alcoholic concoction called Pimms Cup.

"I've been coming for 30 years," said Clive Lambert-Beeson, who won the Wyfold Challenge Cup at Henley 20 years ago. "The object is to eat and drink--strawberries and salmon. We might even do some rowing!"

Businessmen like Lambert-Beeson take advantage of the regatta to invite and impress business associates.

The regatta was somewhat marred this year by the withdrawal of three American teams--Harvard, Yale and Brown--from the prestigious Grand Challenge Cup. Harvard, which won the Cincinnati Regatta, was eagerly awaited, but training conflicts apparently kept the crew away--despite some speculation among Britons that "the Yanks dropped out so they wouldn't get killed."