Some people say that playing tennis on grass courts is an art. Others contend it is a craft; still others a science, albeit an inexact one. Undoubtedly a combination of the three, it is unfortunately a dying skill.

The indisputable fact is that not much tennis is played any more on the surface on which the game was born. Consequently, the technique best suited to turf, with its fast, low, skiddy and uneven bounces, is increasingly unfamiliar to the modern generation of top players.

Indeed, many of the world's best play on grass only three or four weeks a year - at Wimbledon and the couple of English tune-up events that precede it.

Until 1974, three quarters of the traditional Grand Slam, the Australian, Wimbledon and U.S. championships, were played on grass, and each had a series of grass court tournaments leading up to it.

The switch of the U. S. Open to clay in 1975 (another shift, to hard courts, is scheduled this year) signnaled the end of the grass court era for big-time tennis.

The entire U. S. summer circuit changed with it, and around the world most pro tournaments came to be contested on surfaces with which the bulk of recreational players, rather than aristocrats, can identify: clay, cement, cushioned hard courts, indoor carpets, and a variety of synthetics.

Now only Australia and Great Britain remain bastions of grass. Even there the number of tennis lawns is dwindling, despite the undeniable esthetic pleasures of playing on the "all-natural surface," because good grass courts are costly to build and maintain.

Tennis as played on grass is a different game from that seen at most contemporary tournaments, where back-court play and rallies of 20, 30, 40 or more strokes are common.

Slow court tennis tends to be trench welfare, a gruelling battle of wits and stamina. The grass court game is, by comparison, a constant blitzkrieg - all-out attack, faster and more power-oriented, sometimes as stark and numbing as the concussive beat of a sledgehammer and other times a sublime test of reaction and athleticism.

"Two strokes, the service and volley, are often tediously dominant. All is split-second timing," Rex Bellamy, tennis correspondent of the London Times, has observed. "In its own way, this powerful game can be laudable, even exciting. But it also be a crashing, bashing bore.

"Grass courts exalt strength and reflexes, both admirable qualities, but not to the exclusion of the more imaginative tactical pleasures of the game."

When accomplished players meet on a good grass court-and Wimbledon's renowned lawns are among the truest in the world - the result can be a breathtaking spectacle, however.

"The tempo is always changing. When the ball bounces, you never know for sure what is going to happen," says Billie Jean King, six times singles champion at Wimbledon and the No. 5 seed among the women this year.

"I think it takes a better athlete to win on grass because you always have to adjust more quickly, in the middle of a stroke. It's not the best test of tennis, but it may be the toughest."

The best play on grass always is not to let the ball bounce if given a choice, since it may do so capriciously. Thus, serve and volley is the almost universal rule of thumb. Command of the net is important.

Just as serve is a critical stroke, so is return of serve, especially since a single service break often decides a set.

The low, lickety-split, erratic bounce on grass dictates fundamental technical on tactical axioms.

The most effective strokes on grass are not those hit with high-bouncing topspin, as on clay, but with slice, underspin that keeps the ball low.

Players with big swings have to shorten them, disposing of the flourish on their wind-up and follow-through, because otherwise they do have time to executive their shots. There is a premium on taking the ball on the rise and moving forward, inexorably toward the net.

"You have to adjust your whole game to the lower bounce," says King, who acknowledges that grass court virtuosi are becoming almost as scarce as qualified groundsmen.

"You serve more slice, especially on the second serve, so that the ball doesn't sit up for your opponent to take a whack at it. Drop shots and drop volleys are effective because they die in the soft grass.

"Generally speaking, you chip a lot more than you would on a slow court. If the ball comes up, you can topspin it, but you have to pick your spots.

"You have to get a high percentage of first serves in, and follow them to the net. Very few players can stay back and win with ground strokes on grass. You have to go in.

"You expect short points," King continues. "You make every shot expecting the next one to be either a winner or an error. You have to put your volleys away, not play them safe, and go more for deep volleys than angled ones."

A dry grass court gives good footing, a wet one is slippery and treacherous. That is one reason play begins late at Wimbledon, 2 p.m. every day, after the morning dew has been fully evaporated.

"You've got to bend you knees and run quickly, with a dash rather than a steadier kind of footwork," says King. "On grass your first two steps have to be quick, or else you'll never reach the ball."