LONDON (AP) _ Five quiet Americans graced the manicured lawns of the exclusive Hurlingham Club last week week, soothing balm to the British sporting establishment two weeks after Hurricane McEnroe had blown through Wimbledon again.

The setting was quintessentially English - in the grounds of a manor house on the banks of the River Thames, striped tents dotted around the generously- shaded grounds, tea cups tinkling alongside the discreet sparkle of champagne, stooping colonels coughing apologetically through silvery moustaches.

The sport was croquet, obscure as it is delightful. A bit like the players, really.

Tremaine Arkley, Archie Burchfield, Jerry Stark, David Collins, Peyton Ballinger - these are not names to excite fans in the manner of tennis superbrats and other sporting millionaires. Perfect ambassadors for the unknown, they are courteous to a fault.

''Yes, it's not exactly a sport riddled with controversy,'' says Ballinger, one of only two women competing at the inaugural world singles championships and one of only four professionals in the United States.

''There are about 500 of us, I guess, who play croquet in the States, mainly in clubs and resorts.''

Ballinger coaches at the PGA National Resort in Palm Beach Gardens, Fla., and admits to making a ''comfortable living'' from a sport that few have ever seen and even fewer understand.

''Sure, it must be a mystery to the outsider but it's very skillful, believe me,'' said Ballinger.

On a surface the size of four tennis courts, players use a mallet to knock a hard ball the size of a small coconut through hoops that allow only 1-32 of an inch margin of error. They also have to put the striker ball in either an advantageous position for thir next shot or as far away as possible from their opponent.

Arkley, from Indepenence, Oregon, embarked on further explanation before halting to inquire: ''Confusing, right?'' Right.

Nonetheless, the Americans, who have been playing this ancient game for only a dozen years or so were not completely embarrassed in this tournament.

Arkley, partnering an Englishman, advanced to a respectable place in the doubles and the best American, Stark, from Phoenix, Arizona, at least made it into the runners-up tournament before losing.

In a test match against England in April, Stark, who disguises his neat sense of touch inside a bulky 6-foot-3 frame, beat the English star Mark Avery.

The others - Burchfield, from Stamping Ground, Kentucky, and Collins, from Beverly Hills. California - were gracious losers at Hurlingham. Some people wait five years and pay $1,600 a year to join this club; at least those with a mallet got in for nothing and didn't have to queue.

''We'll get better,'' said Ballinger. ''As more players take up the sport, standards will improve.'' But even this enthusiast admits that croquet's one brief flirtation with a wider audience did not make for electric entertainment.

''The video company did a great job with it, different camera angles and all, and good commentary but it was never shown.'' she said.

''I'd sure like to get a copy of that tape.''

It would certainly gather novelty value, a little short of the recognition the sport's dedicated participants might hope for.

So obscure is croquet, even the game's historians are unsure of its origins.

David Foulser, an English international player, said: ''It was first played here in 1861 and we think it came from Ireland.

''But a similar game in 17th century France, called pell mell, may have been the original. And croquet is a French word.

''The first British Open was played in 1867 and it popularity grew among aristocrats, when it did live up to its image of vicarage lawns and genteel tea parties.

''Wimbledon was the first major club and there is still a croquet court there, although tennis took over there a long time ago.

''Croquet went through decline after the First World War but the game has revived since the last War, due largely to the exceptional skills of one man, John Solomon.

''He is indisputably the greatest croquet player of all time, winning more titles than anyone else, 50 in singles and doubles between the late 'forties and 1978.

''We're thrilled to see the involvement of the Americans, although there is some consternation that they have adapted the rules to suit their game.

''The rules introduced by Jack Osborn, the past president of the American Croquet Association, stifle aggression. It's caused a lot of trouble in the sport.''

What? Croquet War Breaks Out At Hurlingham? You cannot be serious.

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