Tracy Austin and Pam Shriver have played nine times in junior tennis tournaments since they were 12 years old. Austin has won all nine. But don't jump to any conclusions.

They are 16 now, both ascending stars and certified overachievers. Tonight they will play for the first time in an adult tournament.

"Maybe if I win this one," Shriver said with the grin that so naturally lights up her wonderfully expressive face, "I can say that I'm ahead in our rivalry."

A sellout crowd of 5,000 is expected to witness their quarterfinal match in the $125,000 Avon Championships of Washington at George Washington University's Smith Center. The sense of anticipation is delicious, because Austin vs. Shriver is potentially the rivalry of the 1980s in women's tennis, heir to such majestic duels as Margaret Court vs. Billie Jean King and Chris Evert vs. Evonne Goolagong.

It is even more fascinating because of the contrasts of personality, temperament and style of play.

Austin -- who breezed past Diane Dcsfor, a Phi Beta Kappa graduate of the University of Southern California, 6-2, 6-2, in her second-round match yesterday -- is 5-foot-3, expressionless on the court, and errs on ground strokes about as often as Evert.

Some people think she is an Evert clone, but that is nonsense; Austin enjoys going to the net too much.

Shriver, who had yesterday off and went back to classes at the McDonogh School in Baltimore, is 6-foot-1, demonstrative and a born net-rusher. Her ground strokes need a good deal of improvement, but her serve, volley and overhead are as sparkling and spectacular as fireworks.

"If you could graft the best parts of their games together, you'd create a monster that nobody could beat," Billie Jean King, who is recovering from surgery on her left foot, observed last night. "It's amazing how opposite their games are.

"In the short term, you can't expect too much from Pam because she's trying to get through two years of school in one, while Tracy is just taking it real easy -- a couple of weeks on the tour, a couple in school. Pam's style of play takes a lot longer to jell, too."

For now, however, the prospects are tantalizing, and tonight's first meeting in a pro event all the more fascinating because of a quirk of history. Even in their rise to international celebrity there is a graphic contrast.

Austin was long heralded as a prodigy. The youngest of five children in a tennis-playing family -- her sister and two older brothers have played professionally -- Austin was on the cover of World Tennis magazine at age 4.

She won 27 national junior titles in singles and doubles, starting at age 10. In 1977, at 14, she became the youngest player to compete at Wimbledon and the U.S. Open, and reached the quarterfinals of the latter.

Shriver started much later, taking up tennis seriously when she was 11. She was one of Austin's whipping girls in the juniors, never winning a national title, but blossomed suddenly last summer and became the youngest finalist in the history of the U.S. Open in September.

Her semifinal victory there over Wimbledon champ Martina Navratilova -- the top seed here and a 6-4, 6-3 victor over Ruta Gerulaitis last night even though she was far from sharp -- was perhaps the biggest major tournament upset in the history of women's tennis. It was also the first time Shriver had gone further than Austin in a tournament.

Tonight's meeting is their first since the final of the National Girls 18 championships at Philadelphia last August, but Shriver does not think that her stiriing run to the Open final a month later will help against her demon contemporary. It may have elevated her stature in the eyes of the world, but not in Austin's.

"Tracy won't all of a sudden be in awe of me just because I got to the final of the U.S. Open, so that won't change anything -- unfortunately," Shriver said after her second-round victory Tuesday over another promising teen, Hana Strachanova of Czechoslovakia.

"I think a lot is going to hinge on my serve. I hate to say that because it puts pressure on it. But we'll just see how it goes."

The best match played yesterday was Ilana Kloss' 6-4, 4-6, 6-4 victory over lean and athletic 19-year-old Anne Smith after Smith came back from 0-5 to 4-5 in the final set. It was rather overlooked in all the hoopla about Austin and Shriver.

Kloss, 27, aleft-hander who was outplayed but saved herself repeatedly by slicing her serve wide to Smith's backhand corner on big points, is in the semifinals of a pro tournament for the first time ever. Before this week, she had never even won a match on the winter tour since 1974.

Kloss won the 1976 U.S. Open doubles and a flock of other doubles titles with fellow South African Linky Boshoff. She has raised her singles ranking from No. 140 to No. 33 in the last six months, and this time she played a resourceful match, relying on her touch and tactics.

She has a greater appreciation of the possible than Smith. She knows what she can and cannot do, and plays within herself, thoughtfully, shrewdly setting up points, keeping the ball in play until she can force an error or sneak to the net.

Smith, on the other hand, is a wonderful talent who has not yet harnessed her hard-hitting game. She tries to make her shots too bold, and leaves little margin for error.

Kloss now has a day off, and will play the Austin-Shriver winner in Saturday's semifinals.

'I haven't played either one of them before," she said, 'but I've heard of them both. I'm looking horward to it. I have nothing to lose."