PROFESSIONAL golfers are as durable as a favorite old putter. They go on for decades, losing their hairline and their waistline, looking less and less like athletes. And still they keep that sweet, compact swing, as if it were a gift apart from the rest of them. By contrast, consider the short and speedy generations of the professional tennis player. John McEnroe at 29 - an age when a golf pro is just mastering his irons - was the old man at the French Open last week. None of the four semifinalists, averaging 21 years of age, had been born when Jack Nicklaus, still a force on the fairways, won his first Masters tournament in 1963.
Such is the difference between a sport where nobody runs and a sport where nobody walks.
Still, the four tennis tots who reached the men's semifinal in Paris are graybeards compared with the women semifinalists - teen-agers all.
Even so, the semifinal match in which Steffi Graf of West Germany defeated her doubles partner, Gabriela Sabatini of Argentina, had a bit of the air of a replay. Though both women are only 18, they already constitute ``archrivals,'' in the clich'e of sports hype. Both are accustomed to being winners - particularly Graf - and their self-assured faces, their experienced eyes, show it. Sabatini possesses the early maturity of classic Latin beauty, looking a little like a young Sophia Loren - curiously combining this with the rolling walk of a jock. Graf's face is all determination, discipline, character, projecting the fitness of a body that looks as if it came to the tennis court straight from a Nautilus machine.
But the other semifinalists, Natalia Zvereva, 17, of the Soviet Union and Nicole Provis, 18, of Australia, are a different matter. Provis has a schoolgirl's chubby face, with innocent blue eyes set off by a blond ponytail. When she misses an easy shot, she walks away with a sulky, head-down shuffle, as if she were going to be late for school and is pretending she doesn't care. When she misses a really easy shot, she shapes her mouth in a pout - as if she had forgotten to do her homework, too. An erratic streak can drive her to place her racket on her head as a duncecap.
Zvereva, who defeated her - just barely - seems equally the schoolgirl, but of a different order. She is thin, quick, nervous - the student who, from sheer energy or anxiety, is a natural squirmer. Her short haircut gives her the unisex look of a 12-year-old. When she serves, her eyebrows arch upward like a roof above her squint. Just before she hits the ball, her mouth forms a tiny O as if to scream. When she loses a point, all this intensity crumples, and she appears about to cry.
Not to worry. These are child-impersonators, concealing a precocious mustering of muscle and will-to-win.
The kid tennis phenomenon is hardly new. Chris Evert and Jimmy Connors began as the toddling extensions of ambitious parents. But the little winners seem to get to Centre Court sooner and sooner, and the crowd just loves these infant prodigies. It eats them up - and spits them out at about 22.
Tennis is not child labor - not at those prices. But the cult of the winner - the pressure to be No. 1 - has produced its quota of burned-out millionaires in their 20s. Above the bashing games of Graf and Sabatini hover the ghosts of Tracy Austin and Andrea Jaeger, former child champions, whose overtaxed bodies and wills made them has-beens at the age other women are just graduating from college.
The teen-agers now taking over tennis make up an extraordinary corps of Spartans, junior grade - not to forget 18-year-old Andre Agassi on the men's side, who especially delights the spectators by acting out the fantasy that it's all in fun.
As the next generation of prodigies, at the age of 10 or so, already moves from airport to airport, from tennis court to tennis court, setting new standards of skill, what gets left out of their lives? You could write a parable of lost childhood on the theme and call it ``Amadeus'' in honor of the prodigy of prodigies - only this time you'd have to forget the music.
A Wednesday and Friday column