"Your line, your LINE, YOUR LINE! YOUR'RE GONNA CROSS AGAIN," the adrenalin-charged voice is yelling as the rollicking pack of eight men and horses tears into hearing range of the spectators.

"Since these ponies travel between 35 and 40 miles per hour," booms the miked voice of Louis Traxel, games announcer, "the object of the rules is to keep the horses and players from killing each other."

"Frankly, Amelia," comes the soft drawl of a middle-aged onlooker, "I can't help wondering what the horses think of all this."

On almost any fine Sunday afternoon,between the months of April and November, there occurs in the shadow of the Washington monument a bit of sporting theater, which, when trapped in time by the eye of the camera or the memory of a beholder, provides one of the city's most unusual and least captialized-upon post cards. The image is of green lawns, galloping ponies and intrepid riders, all veering towards a line of trees beyond which can be glimpsed the slow traffic of passing cars, cricket players and just occasionally, a pedalboat on the Tidal Basin. The reality of course is a polo game; specifically, the weekly match between the Lincoln Mall Polo Club and visitors -- scheduled, t.b.a., or hastily rounded up and pressed into service as well as into what are oftentimes tattered team jerseys.

The Lincoln Mall Polo Club, more formally known as the National Capital Polo Association, has been quietly enchanting tourists since it was established in 1968. The natives, however, are something else. Even the most broadminded area sports fan, able to reel off the names of West Coast foot-base-and-basket-ball teams, not to mention Canadian hockey players and Guatemalan jockeys, would have difficulty coming up with the title of one local polo club. Polo, it's generally held, is picturesque -- also ritzy, a private indulgence of overseas royalty, wealthy Latins or homegrown effete snobs and, therefore, runs the assumption, sort of, well, you know, namby-pamby. An athletic teaparty on turf.

Hobbled by this perception of elite chic and tettered to a shoestring budget, the LMPC has nevertheless played over 500 bone-crackingly aggressive games. It's hardly an accident that General George Patton periodically rode across the river from Fort Myer to play polo on a field that's a stone's throw away from today's turf. Nor that the cavalry encouraged its officers to take up polo. The game, like chess, is a battlefield in miniature. An image supported by the sight of rangy farmers, combative doctors, stockbrokers, employment agents, Marine pilots, small businessmen and innkeepers, all caroming down a green the size of eight football fields, wildly brandishing one-pound mallets in a effort to knock a 3 1/2-inch ball between eight yards of goalpost and casually clobbering opponents, horses and themselves in the heat of the struggle. Gentlemanly, polo might be, but gentle or genteel it isn't.

On the one hand, words like "tough," "aggressive," "as competitive as football" are used to describe the game's physical demands; on the other, "costs no more than a sailboat" or "same as playing country-club golf" are parallels summoned repeatedly to expain demands on income. Truth seems to lie more on the side of rough than it does of cheap. Which doesn't mean polo's only for the rich; just that it's certainly not for the poor.

It's the creatures that cost. A player has to have a minimum of three horses (a fresh horse for every other chukker, or period of play, in a six-chukker match), all of which have to be fed, housed, tacked up and hauled to games in a gas-guzzling truck-trailer. Stalls regularly have to be mucked out, horses exercised and vets called in to repair ravages endured in a game aptly referred to as hockey on horseback. And when the season's over, you can't, like a bag of clubs, stuff the animals in the back of a closet or roll them into drydock. They keep on eating.

But how much exactly does playing polo costs? That seems to depend.

"If you've got $12,000 you can get yourself set -- pick up some horses for $1,500 to $2,000," says Jack Kinslow, a player who took up the game about a year ago.

"It depends on how you play," comments Jack Whittenmore, a young stockbroker who's been playing the game since he was 13. "You can go into polo in any way, just like golf. Polo can cost you easily $150,000 a year. It can, but it doesn't have to. Right now a lot of people around here are putting money into horses. I know someone who just took out a second mortage on his house to go to Texas and buy ponies."

If it's the horse that makes polo a pricey game to play, it's also the horse that defines polo, gives it an edge of speed, roughness and interest over other team sports. A player has not only to control his own muscles and instincts but those of an idiosyncratic thoroughbred, weighing a thousand pounds and overly excited about the idea of chasing a ball up and down the field in the hot sun. It stands to reason: If you can't ride well, you can't play polo.

But if you can? Then you still have to be able to hit a ball with a four-foot stick while hanging out of the saddle, as an opponent uses wits, strength and his horse to harass you. In a tactic called riding off, a member of one team atempts to force himself between a member of the opposing team and the ball. The effect is of a muscular sideswipe at, maybe, 35 miles an hour; the effort, however, seems to illustrate why polo is less a pastime than an addiction -- it's outrageously competitive.

The unlikely combination of equestrian skill and precision hitting with a contact sport that demands careful team-work drives habitues to insane lengths and improbable playing ages. Edar Staples, nearing his seventh decade, still hauls six or seven horses to Washington every Sunday in season from his farm on Polecat Creek outside Richmond in order to play polo. Tommy Leonard regularly hies up from North Carolina. General Traxel, who began playing at the University of Illinois in 1921, steadfastly plans to referee again once he's fully recovered from an off-field accident.

Jack Whittemore summed up the attitude prevailing down at the Lincoln Memorial Field when he assured a listener that "there are other things in my life besides polo," stopped to think about it, then added, "but not much."

The lure of polo extends well beyond the confines of a heated match, however. So does the ardor it inspires. John J. Sted may have hung up his mallet quite a few years ago but that didn't cut down the hours he devotes to what players routinely refer to as addiction. For, in lieu of playing in games, Sted, as executive director of the LMPC, produces them. And, as with any producer of a regularly scheduled action pageant, the worries overwhelm the tasks.

Sted worries about low-flying helicopters that spook the ponies and about encroaching baseball teams that rub homeplate bald spots on the field and litter it with soda fliptops which can wedge in the frog of a horse's hoof and make him lame. He agonizes over the rising price of polo balls ("$86 a gross when I started," he says with a forlorn shake of his head, "now it's $155 for 100!"); hippies who once burned the field sideboards; whether it will rain; the French taste for horsemeat and how it's helping drive up the cost of thoroughbreds; the 120 tons of mushroom soil he cadged from the circuit governor to improve the turf; "dead" dogwoods that slice off an edge of the field, posing a hazard to speeding riders; who's going to referee; the conditions on highways that horse-hauling players must travel; how to pay this year's debts with next year's dues, and how to get more sporting people interested in both cheering and playing the game.

In fact, the pursuit of better players is partially responsible for the radically changing face of polo in this country. Players are ranked by a handicapping system that begins with -2 and, like beauty in a recent film, reaches perfection at 10. It isn't unusual to come across a seasoned player with a zero handicap; two-goals is considered quite respectable and four about as high as anyone who makes a living at a desk could hope to reach. Currently there are no 10-goal players in the United States; only five in the world and all five are from Argentina. This rankles. And helps explain the push that's on to popularize polo.

In Florida, the first real estate development in the world to be centered around polo opened last year under the financial sponsorship of an electronics corporation, Gould, Inc., whose chairman William T. Ylvisaker, is a long-time player of the game. With its nine fields, deluxe condominiums and expansive stables, the Palm Beach Polo and Country Club is one of the most notable examples of polo's rising prominence. But it's hardly the only one. In places as far-reaching as San Antonio, Boca Raton and Santa Barbara, brand-new stadiums and sports complexes devoted to polo have opened in the last year or two. And in virtually every case the men behind the development -- the sponsoring patrons -- are avid players.

Washington's no different. The individual emerging as the acknowledged patron of area polo is Joseph A. Muldoon Jr., a tall, brawny lawyer who took up the game 10 years ago after one too many hair-raising steeplechase spills. He formed his own team, Gone Away Farms, hired a pro to coach and play and hit the tournament circuit. When the old Potomac Polo Club folded, Muldoon bought up 700 acres of sod fields near Seneca, leveled them to create several polo greens, absorbed Potomac's members (and its name) as well as the Woodlawn Club's players and, this June, began sponsoring Sunday afternoon games. His plans are to erect a stadium and a clubhouse and attract a following of sports fans. His aim is to upgrade polo.

"I want to get the best players together in one place," says Muldoon determinedly. "The only way to improve polo is by having good players play with even better ones. And in any sport, spectators move it up."

There is, however, a less altruistic reason why a wealthy player will erect a stadium and/or sponsor a team. In polo, amateurs and professionals play together, the sum of their handicaps expressing the ability of any given team. Of the 1,500 players currently registered with the United States Polo Association, only 10 are ranked six-goals or better and none of these, notes Muldoon, are amateurs. With enough money, therefore, a well-heeled player can hire high-goal pros to support him on the field, in which case, "it's like owning the Washington Redskins," says the ultra-competitive Muldoon, "only you get to play with them on Sunday."

If Joe Muldoon embodies the irresistible combination of forces -- money and passion -- currently being aimed at an alteration of the image of polo in the U.S., the Lincoln Mall Polo Club, with its light dues ($50 a year per player), easygoing atmosphere and open invitation to players and spectators, symbolizes a less flamboyant aspect of the sport that's prevailed throughout its 3,000-year history: avid riders who, regardless of personal assets or public acclaim, just pick up and play the game. Season after season.