BEFORE we talk about the wheezy air conditioning, straining to cool the courts to the temperature of a mild day in Bombay, before we see Howard Gary wrapping strips of silver duct tape around his hands and fingers, even before we hear Jack Weintraub tell us that the "golden geezers" are declining in numbers, the first thing to say about handball players here at the Westside Y in Manhattan is the obvious.Like their counterparts all over the country, they play regularly. So it's 6:30 in the morning. So it's a little warm outside (75 degrees already). It could be snowing, raining, or sleeting. Go ahead and serve. "People here play at least twice a week, often three and four times," says Richard W. Meirowitz, who by 10 a.m. will be busy in a different court game, practicing law. Handball, the closest thing to boxing without having to hit someone, is played by hitting with your hand a bright blue ball that costs $2, weighs 2.3 ounces, and measures a tad less than 2 inches in diameter. Equipment is simple: a pair of $15 gloves and, as recently mandated by the United States Handball Association (USHA) for tournament play, eye guards. To the uninitiated, play looks simple: Hit the ball against the wall or walls until your opponent fails to return it to the front wall before it bounces twice. But handball, like tennis or its nearer cousin, racquetball, is far more complicated than that to those who know and play it. A defensive player uses the ceiling and a closed-fist shot more. Everyone wants to command the center of the court. Deep and in the corner to the side of your opponent's weaker arm is always a sweet shot. Grunts, dives, tantrums, arguments (not to mention backhanded compliments about the other guy's game) round off any court action. Ambidexterity is the sine qua non of handball. A quote attributed to the late, famous handball player Jim Jacobs (a former trainer of boxer Mike Tyson) says it best: "Your right hand is the sword, your left hand the shield." If you can't play equally well with either hand, that's a weakness, and with "any weakness, like in any court game, you'll bang the weakness," says Ted Gewertz, one of the golden geezers (as they call themselves), who has played for more than 25 years. Handball players are not known for their mercy, says Mr. Weintraub. What strategy does he espouse? "Very simple: You [just] hit the ball where it ain't." In the four-wall version, "you have to make the back wall your friend," he says: "You got to have a temper. Once you get on a court, it's a war." A key difference between handball and the more popular racquetball, says Mr. Meirowitz, is the need to play regularly. Unlike racquetball, where you can sit out for a week, even a month, and come back and play a good game, "you cannot do this with handball. You have to play regularly and stay in shape, like boxing or karate, or you can't play, at least play well, he says. Watch a game between skilled players and it is quickly apparent that the better player moves the least. Jumping, diving, twisting shots, however impressive, simply mean that one player is dominating court position, placing the ball better. Since the velocity of a shot is a factor, the player who is set on both feet as he hits the ball not only has the better chance of hitting it harder, but of expending less energy doing so. After hundreds of volleys, the comparative reserves of strength in evenly matche d players often determine victory. Students of archaeology know that handball was around for thousands of years before it turned up in Ireland sometime in the 10th century, where it was called Fives, after the five fingers of the hand. Paintings in Egyptian tombs show that the pharaohs played the game before the birth of Jesus. Handball emigrated to the United States in 1882 when Irishman Phil Casey brought the game to Brooklyn. Firemen (handball is essentially a male preserve) found the game just the sport for in between blazes. By the turn of the century, the game had moved into YMCAs and other urban health clubs as well as schoolyards and city parks. THERE are more than 20,000 four-wall courts in about 2,000 venues in the US, according to the USHA. The four-wall version, with its 20-by-40-foot court, and 20-foot ceiling, is played in YMCAs and sports clubs all over the country. The East Coast is home for most of the country's one-wall courts. That game is played on a 20-by-40 foot court, especially in New York, and nearly always outdoors. There are some three-wall variations of the game as well. Devotees of one-wall and four-wall handball banter about the fine points between the two games. "In one-wall, three-quarters of the game is the serve," says Weintraub. "You don't need too much of an opposite hand." "Au contraire," says Brooklyn's Joe Durso, USHA one-wall national champion for the last 10 years. While conceding the serve may be more important in one-wall, "the game of one-wall is physically harder because you have to be much more accurate. The wall is much smaller, he says. A denizen of the Coney Island courts, at 6 ft. 1 in., Mr. Durso is tall for a game where ground-hugging is an asset. He also is not shy about his talents. m the king. Put me on TV and handball will arrive the way tennis did when Billie Jean King played Bobby Riggs," he says. He has been known to challenge two players simultaneously - with his right hand tied behind his back. According to a recent Niel-sen Sports Participation Poll, there are 2.5 million handball players. But Vern Roberts, executive director of the USHA, says "real" handball players number a far fewer 50,000 - a "real" player being "somebody who plays once or twice a week, religiously." The USHA reports 50 state organizations that sponsor handball competitions. For devotees, hand-ball is a lifelong affair. The age-group categories at the 200 tournaments held nationwide each year (12 major ones) range from 11 to 75. The greater number of older categories may point to a serious problem facing the sport. "Handball players are a dying breed," says Mike Spezzano, New York City area sports fitness director for the YMCA. "New Y's in our area are not even putting in four-wall courts," he says. The economics just don't pay. "That's a lot of space for two guys to play," he says. Put an aerobics studio in the same space and hundreds can work out instead of 30 handball players a day. On his way to the shower, Weintraub acknowledges that in cities, "the girls [and men, he later adds] playing racquetball keep us alive." Their numbers keep the courts in use. They just haven't realized handball is a much better game, he says.