Andrea Jaeger, just turned 15, was up in the players' tea room at the All England Lawn Tennis and Croquet Club this afternoon, after beating Virginia Wade to become the youngest quarterfinalist in the history of the veneralbel Winbledon Tennis Championships.

It was nealy 4 o'clock, too late for hot lunches to be served., Andrea -- who is 5 feet 3 and weighs 97 pounds, but has the appetite of a weightlifter -- hadn't eaten since breakfast. She devoured two plates of strawberries and cream the same way she hits her backhand -- with two fists.

On the Centre Court, she had impressed everyone with her poise, her composure, her presence. This girl is cool, feisty, unintimidated -- a born competitor.

But in the tea room she was just another delightful 15-year-old girl, joking with her sister, wondering if there was time to go out for a pizza before her scheduled mixed doubles match with Coach Owen Davidson, telling a friend how well she's been doing at "Space Invaders," the pinball game she has played incessantly at an arcade next door to her hotel.

"She's deferent off the court -- a normal girl, a really nice kid," said her 17-year-old sister Suzy, a lesser tennis player but a nice kid herself.

"The thing with Andrea is that she is so competitive, at everything -- soccer, checkers, any kind of sport or game. She even wants to be the first one to the elevator, things like that."

Roland Jaeger, a former soccer player, cyclist and amateur prize fighter who has had to battle for most of what he has in life, is somewhat obsessed with competitiveness. He grew up on the German side of the Swiss border, came to America and worked at various jobs including laying bricks and running a restaurant, before he became a successful teaching professional. He worked hard, and he taught his daughters to do the same. He talks about playing tennis matches "down to the nails," and that is how Andrea plays them. p

"She's way, way beyond her years.She's got a 25-year-old head on a 15-year-old body. She knows what to do. If you give her advice, she remembers it. She sticks to the game plan and never, never gets nervous."

Davidson, 37, a warm and perceptive fellow, reached the semifinals of Winbledon in 1966, partnered by Billie Jean King to four mixed doubles titles here, and was the pro at the All England Club and Britain's national coach for four years.

He has been working with Jaeger for only a month, but she has impressed him enormously with her skills, her attitude, and her aptitude.

"It's the same way the first time you see any of the great ones. remember the first time I saw Chrissie Evert play. I could see this incredible presence on the court for such a young kid," he said. "The same way with Tracy Austin. There was this unbelievable control of herself and her surroundings. It's the same way with Andrea.

"It's an inner presence, almost like a charisma, and other players don't have it. You have to be born with it. She has this immediate instinct about what's the right thing to do on the big points.

"There are very few players in the world who play better in matches than they do in practice. The ones who do rise to the top. You watch Andrea even now, and she plays in the big points unbelievably well, as if she was born to be out there. Even when she loses concentration -- she senses immediately when there's danger. When she does she plays better. That's a quality so few people have."

Ilse Jaeger, Andrea's mother, said that she was more jittery sitting in the guest box on Centre Court, watching, than her daughter was playing.

"She's never nervous," said Mrs. Jaeger. "She's always liked to be the first, the best, the leader. Nothing fazes her. In school, she loves to get up in front of the class and give reports. I guess it comes naturally to her. uShe's always been like that.

She has the qualities of the great ones.