Every year at Wimbledon, the U.S. Open, and the French Open, young players emerge who experts contend can be No. 1 someday. The following season, they invariably struggle with unreasonably heightened expectations.

Part of the problem is that tennis, at present, is so true to form. John McEnroe and Martina Navratilova win so often that the media are hungry for fresh subjects. Success at Wimbledon and beyond for a rookie, though, can be evaluated objectively. Physically, quick hands and feet are needed to cope with the low, skitting bounces on Wimbledon's grass courts. Few young players with little previous grass court experience can make the transition in time. To be sure, no unseeded player has won the men's singles title.

This year, the newcomers most often mentioned were Boris Becker, the 17-year-old West German, and Gabriela Sabatini, the 15-year-old Argentine. Sabatini, the 15th seeded player, must wait another year, however -- she was ousted Saturday by Catherine Tanvier, 6-7, 6-4, 6-1.

Among the men, Becker is being touted as a long shot here. He won the Queens Club tournament two weeks ago and is coached by Ion Tiriac, mentor both to Ilie Nastase and Guillermo Vilas. Becker has the hands to handle erratic bounces but his court coverage cannot keep pace with the shots of McEnroe or Jimmy Connors.

Almost any analysis of success at Wimbledon shows a high positive correlation with a return-of-serve percentage in the 40s for first serves and the 60s for a second serve. Only one or two first-timers could produce such results on this least-used surface on the men's tour.

Another critical figure is break-point percentage. Since it is easier to hold service on grass than on any other surface, those who can break on grass are likely to do well. McEnroe's percentage of break points won is in the high 60s. Anything over 50 percent is considered good.

Women's competitors have a different set of problems. Only a handful serve and volley here, so the service return efficiency is slightly less important. Overall consistency, a low unforced error ratio and court coverage are the keys to winning. Since first-time female players here invariably are two to three years younger than their male counterparts, court coverage becomes the predominant factor.

Sabatini is the most discussed newcomer here. Billie Jean King says Sabatini "has all the shots, is well-coached, and has good instincts, but she's just not fast enough to run down Chris' (Evert Lloyd) ground strokes or Martina's volleys. Her legs are not strong enough yet."

On any other surface where the bounce is higher and slower, Sabatini would have a chance. Three weeks ago at the French Open, played on slow clay, she reached the semifinals.

The slick grass here also can baffle young but experienced players. Eighteen-year-old Aaron Krickstein is ranked in the top dozen and was seeded No. 10 here. Yet he lost in the first round to Bud Shultz, who had not played a singles tournament until he was 20. Krickstein is not a serve-and-volley player and had trouble adapting his late backswings to the rapid bounces.

Despite the good press notices and results of Becker and Sabatini, the odds were against their winning Wimbledon this year. This most prestigious of tennis events poses difficulties that veterans find trying. Players with faster foot speed, quicker hands and steadier nerves have tried for years to win.

Young players would do well to watch closely the semifinals and finals of the men's and women's singles. They will see clearly what is needed for victory here: a high return-of-serve percentage and the wherewithal to win big points. Then come back next year older, quicker, faster -- and wiser.