Defending champion Tracy Austin and four-time champ Chris Evert Lloyd -- whom Austin dethroned in last year's final, one match shy of a record fifth successive crown -- today advanced to a semifinal meeting in the U.S. Open Tennis Championships.

Friday's encounter between the modern Queen Mother and Queen Regent of the baseline game -- 15-year-old Andrea Jaeger, who plays her quarter-final against Argentinian Ivanna Madruga on Thursday, is the Princess-in-Waiting -- will be their first since January, when Austin trounced Evert three times in 11 days and sent her into temporary retirement. It could be the most important renewal of a fascinating rivalry.

Austin, 17, was too solid off the ground today for her longtime junior rivel, Pam Shriver of Lutherville, Md., foiling her net-rusing attack to win, 6-2, 6-3.

Evert, 25, who had lost only nine games in four matches up to the quarterfinals, was uncharacteristically eratic before settling down to oust Mima Jausovec of Yugoslavia in a battle of long rallies, 7-6, 6-2.

Evert -- winner of 40-41 matches and five tournaments since returning to competition in May after a sabbatical that she insists was never intended to be as "retirement" -- served for the first set twice, at 5-4 and 6-5.

Both times Jausovec broke back, and forced a nervous tiebreaker that also was dominated by errors rather than winners. Jausovec had set points at 7-6 and 8-7, but netted forehands. She then hit a forehand long to make it 8-9, and after a 17-stroke rally, knocked a backhand approach shot over the baseline to give Evert the tiebreaker, 10 points to 8. Chrissie cruised from there.

Shriver and Austin played in the 19,000-seat stadium of the National Tennis Center, but curiously were scheduled for 11 a.m. By the time people started arriving, Austin was already ahead 4-0, since Shriver was nervous, tight and tentative at the outset.

Shriver, 18, had not played in the stadium since losing to Evert in the 1978 final, when she was the youngest finalist in the tournaments history. After that, she went back to high school, then suffered a shoulder injury that took her intimidating serve and overhead. Injured and discouraged, she plummeted throughout a lost 1979 that reached its nadir when she was beaten in the first round of the Open by qualifier Julie Harrington.

In the six months since she re-built the shoulder through arduous work in the gym, Shriver had put the pieces of her game back together. Now No. 14 in the computer world rankings, she hasn't lost to a player ranked below her since February. But she hasn't beaten a player of Austin's stature, either which accounts for her anxiety.

Shriver got only 55 percent of her first serves in court, which made it difficult to attack. Her slice approach shots were not quite fine enough, and sat up on the slow rubberized asphalt hard court, letting Austin get a good whack at her superior passing shots.

Austin has won all 11 of her lifetime matches against Shriver. The first was in a junior tournament in Columbus, Ohio, when Shriver was 12 and Austin, 11. The most recent, before today, was 19 months ago in Washington, D.C.

"How long will the soap opera go on?" someone asked after the match.

"What, with Tracy and me? Probably a couple of more years, until I can really hit the peak of my game," replied Shriver, who knows it takes longer for her aggressive serve-volley game to jell than it does Austin's more conservative backcourt style.

"She's got about as good a game to beat a serve-volleyer as anyone . . . . For me to consistently beat her, I've got to serve a heck of a lot better than I did today. I never got going on the serve, and when that happens, it puts a lot of pressure on my other shots."

Shriver had game points in six of the nine games in the second set. "The whole time I was so frustrated because I just kept missing by an inch. I felt I was so close to getting back into it, and I couldn't," she said.