THE SERVE explodes off the front wall. In the closed court, it sounds like a big-bore handgun. The ball blurs past to the left, ten inches from the floor, and you wheel after it, soles squealing on the waxed wood, shoulder dipping to dig out the rebound from the back corner and snap the ball up, hard, 20 feet to the ceiling, ricocheting down onto the front and up again off the floor, climbing.

You sprint for center as your opponent goes back, the two of you three feet apart, ducking past, and he catches it in the air and drives a pass down the right side, two inches from the wall, and your jerk, stretch to scoop it off, racket smacking the sidewall, a weak shot, bouncing on three walls and ending up a foot off the floor. Her runs up, cocks his arm back three feet, his racket hisses past your face, you snap your head away, and he nails it right in front, right at the juncture of floor and wall, unbeatable angle, killshot.

One point.

After half an hour, the floor is spotted slick with sweat, both players look like they've been standing in the rain, and the loser's face is the color of corned beef. That's the first game. Two to go.

THERE IS NO more ancient and venerable affinity than that between man and ball.

Ever since the primordial sportsman found that rocks would roll, man has labored unceasingly to find more ingenious and maddening ways to move a ball around. But nothing is recent memory can equal the present ravening mania for racquetball.

Apparently immune to recession and inflation alike, racquetball has become America's fastest-growing indoor sport. This is strange, on the face of it: The national craving to sweat for hours in a plaster closet-with an armed stranger and a ball flying over 100 mph - does not appear wholly rational.

But successful sports are rarely rational (who can explain golf?), and well over 5 million Americans have taken up racquetball in the past 10 years alone. In 1968, the very word did not exist; in 1978, there are some 900 commercial facilities, courts are booked up days in advance and an astounding 17 million balls were beaten dead in the past year alone, according to industry figures.

The most likely reason for the game's popularity is that, as a form of violent catharsis, it is exceeded only by divorce or mudwrestling. What with the frantic scrambling from soft drops to hard passes, the wristwrenching snap of the racket and the constant maneuvering in cramped space, the action will - as the U.S. Racquetball Association's National Coordinator, Terry Fancher, says - "really let your emotions loose."

"There's a lot of agression that's being gotten rid of," Fancher says, "and it can cause agression. It's a confined space, enclosed, it's hot in there, loud, and it can get physical. It's easy to lose your temper." That's why he dismisses a recent criticism in Sports Illustrated - that racquetball games will never be televised until the players "clean up their act" - by conceding, "We let the guys scream a little bit."

And why not? It's precisely that simple predator therapy that has made the game a screaming success. But it has other advantages: It's demanding, democratic, dangerous and all-American.

RACQUETBALL IS at once a hard game and an easy one. It demands more aerobic exercise than any other sport short of serious running or long-distance swimming. A good amateur club player will burn about 600 calories an hour, a pro upwards of 800 - which is why racquetball players regard tennis as a game for the elderly and the terminally fat. But in contrast to the more delicate and strategic squash and handball, it's almost embarassingly simple to play.

With a lively 18" strung racket and fast 1 1/2-ounce rubber ball - and with play legal off the 20'-by-40' floor, all four walls and the ceiling - only a patent imbecile can fail to play a satisfying game of racquetball the first time out. Moreover, in keeping with the American character, the game rewards hostility: Blind animal fury is nearly as apt to produce an unreturnable shot as the most practised finesse.

Simple rules - in effect, the last person able to hit the ball wins the point - combined with accessible equipment (you can hit the floor for as little as $20) and relatively affordable court rates ( $7 an hour is a Washington average) make racquetball an agreeably democratic sport. Although two-thrids of the players are men, as many as 2 million women have taken up the game, and mixed singles are common in club and on campus. In fact, racquetball may be providing a healthy alternative mating ritual to singles bars, as the best and the lightest of the middle class meet in the damp intimacy of the courts.

Indeed, the United States Racquetball Association (USRA), headquartered in Skokie, Illinois, has compiled a demographic profile that targets the average player as a single suburnite in his or her late 20s, with a college degree and a salary around $18,000 a year, who plays twice a week or more.

Manufacturers take an interest in statistics like those, and racquetball satisfies the indispensable American sports criterion: an exploitable market for specialized gear. There are, to your astonishment, special racquetball shoes. (Admittedly, tennis shoes are a mistake - they are built for different stresses, and basketball shoes will generally last longer on hard wooden floors.) There are various lines of racquetball clothing in alarming and intemperate hues, a chromatic riot of balls (black, blue, green and red - at about $1.50 each and seviceable for around five hours of play), and a host of ancillary appliances.

And then there are the rackets. Moon-shot technology coupled with near-infinite consumer credulity have produced a stupefying array of rackets in various shapes, weights and compositions - including wood, steel, fiberglass, aluminum, magnesium alloy and graphite fiber. Although a good racket (for most players, the lighter the better) can be had for under $25, prices go as high as $60.

The agressive nature of the game is nowhere more blatantly embodied than in the brand names of rackets. A shopper finding even the Agressor or Magnum too tame - and perhaps justly contemptuos of something as demure-sounding as the Rebel, Centurion, Boomer or Hustler - may still find a certain phallic-homicidal gratification in the Spoiler, Bullet, Pistol, Vendetta, Enforcer or, yes, the Avenger .

UNFORTUNATELY, the agression that makes such a useful marketing tool also makes a racquetball probably the most dangerous racket sport. Although an early advantage of the game was its safety (gentlemen and executives would not damage their hands while playing, a routine hazard in handball), it's become so fast and so widespread that - in addition to the possibility of sprains, broken bones and dislocated shoulders from hitting the walls - racquetball is now a major cause of eye and facial-bone injury.

A 1976 article in the Journal of the American Medical Association, entitled "Racquet Sports - An Ocular Hazard," reported that there were 3,220 eye injuries in racket sports (tennis included) that year alone. The National Safety Council has not kept records on the latest extent of the damage; but the numbers are certainly swinging upward as the number of players increases. (Although the USRA has published repeated warnings in its magazine, National Racquetball, almost no one uses eyeguards.)

As a result, there is hamburger all over the hardwood. First, the ball itself is dangerous.A professional can hit shots of up to 160 miles per hour, and a good amateur hits around 100. When the ball strikes the back or legs, the result is a bull's-eye-shaped welt that disappears after a couple of days. But striking the face at that speed, the 2 1/4" spehre can pass the bony orbit and hit hard enough to rip the retina right off the back of the eyeball, or rupture the tissue and cause hemorrhage, or paralyze the iris. Some injuries can result in blindness.

And the players themselves are almost as dangerous. It's impossible to play the game right without jockeying for a very limited space at the center of the court, or without looking around to see what the opponent is doing; and inexperienced, stupid or pathologically careless players will strike each other with the rackets. The threat disminishes with expertise, but "it's risky," Fancher admits, "metal racket especially" - and, without the protection of eyeguards, it's not uncommon for a swing to smash the mouth, cheekbone or nose, or to crush the eye socket.

Compounding the pain and humiliation of injury is the Draconian justice of the rules: The struck player is deemed at fault for his own multilation, and the game thus provides no disincentive for recklessness.

But then, danger has never dissuaded Americans from sport; often quite the opposite. That's why pinball is not the national game. But its intrinsic risk in only one element of the national appeal.

UNLIKE ALMOST ANY other racket sport, racquetball is a peculiarly American creation. Its predecessors, handball and squash, are both 19th-century imports from the British Isles. Handball apparently began in Ireland as a low-cost form of competition for those whose lives were already bound by four walls, and whose Celtic genius made a virtue of necessity. Squash is said to have originated in London's Fleet Prison, among inmates whose confined exercise yard led them to create a sort of paddle-and-ball game that could be played in close quarters. Oddly enough, it was squash - the invention of frustrated felons - that developed an upper-class image and clientele in America and was long regarded as the exclusive province of New England brokers who learned it in prep school, while handball spread more widely and developed a more proletarian following.

It was not long, however, before the incorrigible American spirit of innovation descended on the games. In the first decades of this century, there was already paddle tennis, a sort of dead-ball counter-part to real tennis played with wooden paddles. And in the 1920s, according to the USRA history, an enterprising athletic soul named Earl Riskey developed an ungainly new game called paddleball at the University of Michigan to exercise his paddle tennis players on handball courts. The game bounced along for two decades, gathering a modest following (as well as the enduring odium of handball players, who historically have resented the invasion of their courts by what they consider the too genteel and undemanding alternative games).

It remained only for progress and tedium to combine into the modern sport of racquetball. In 1949, Joe Sobek, a bored former tennis pro in Bridgeport, Connecticut, was looking for cold-weather exercise. He had seen paddleball, and decided that it could be a livelier game with rackets and a faster rubber ball. So the game of "paddle racquets" was created, and became an immediate hit at the Greenwich YMCA.

As the game spread, it was played under a variety of names - the most usual was "paddle rackets" - and gradually grew in popularity until 1968, when the Jewish Community Center of Milwaukee put the sport in the public eye with the first major tournament. By then, it had become necessary to form an organization to standardize the equipment, and the United States Gut Paddleball Association was created. Someone must have realized that the title was a public-relations catastrophe, and in 1969 the organizers changed the name to racquetball.

The rest is history-a rapid and impressive history of promotion and marketing that is literally growing by leaps and bounds. An optimistic USRA predicts that by 1980 there will be 14 million racquetball players in the United States, buying some 30 million balls a year.

Whether it happens or not, that's still some racket. CAPTION: Cover by Terry Dale from photos by James M. Thresher. By James M. Thresher.