There were inevitable comparisons today with 1971, the coming-out party of a Sweet 16 named Chris Evert, as soon-to-be ninth-grader Tracy Austin upset No. 4 seed Sue Barker, 6-1, 6-4, to reach the round of 16 in the U.S. Open tennis championships.

Austin, though to be the youngest player ever to compete in the U.S. Championships at 14 years, 9 months, played steady tennis on the stadium court, moving like a sprite and hitting everything back, to eliminate the impatient and terribly ragged Barker in 59 minutes.

Deja vu, the sense of having seen it before, was a common feeling at the West side Tennis Club. "Little Tracy" had people raching back six years for memories of "Little Chrissie" and her sentimental run to the semifinals, 20 years after "Little Mo" - Maureen Connolly - won the title and the hearts of the spectators of 1951.

"Sure it's similar. I thought Chris looked so young at 16, and here's this little punk at 14," said Billie Jean King, conquerer of the youthful Evert and champion here in '71, who today had her hands full in oustings qualifier Sheila McInerney, 6-1, 2-6, 6-1.

"It's a bloody good effort," continued King. "Tracy's great. Like Chris it's all about yet. She's just having a good time. But it's not really fair to say she's like Chris or anybody else. She's Tracy."

Evert - who today won her 109th consecutive match on clay courts, over 20-year-old Helena Anliot of Sweden, 6-2, 6-2 - was asked if Austin at 14 reminded her of herself at 16.

"Her tennis game does," the champion of 1975-76 and No. 1 seed said. "I think we have pretty different personalities. I never had a smile on my face that often. She seems to be pretty outgoing; I was more reserved.

"But definitey when I watch her play tennis . . .It's the same backhand. She has a better volley than I did at that age, but otherwise we're pretty similar."

Austin - 5 feet tall, weighing 90 pounds, with her blonde hair in bunches (not pigtails, please; they're not braided) and a mouthful of braces - is a month younger than Jeanne Evert, Chris' sister, who when she first played Forest Hills in 1972, and two months younger than two-time champion Sarah Palfrey was when she debuted in 1927.

Her game is still developing, of course, and will change as she gets bigger and stronger, but even now she has a mature approach.

"She's an agressvie little girl. She loves to get to the net and volley. Everybody talks about her ground strokes, but Ithink her net game is more amazing," Austin's coach, Bob Lansdorp, said today. "Still, she knows that on clay she has to stay back and be patients. She knew that was how to play Sue Barker."

Austin went on court with a simple strategy: to play steady to Barker's backhand. "I had heard she had a great forehand."

As it turned out, Barker was shaky on both sides. From the opening game - which Austin won after four deuces, saving a break point with an ace down the middle - she made an embarrassing number of unforced errors, 18 on the forehand, 17 on the backhand. "If anybody make that many errors against her," said Lansdorp, "Tracy's going to beat her."

Austin now has a good chance to get to the semifinals, where she likely would meet Evert in a peculiar quirk of history. She is scheduled to play Romanian Virginia Ruzici on Monday, and then the winner of No. 5 seed Betty Stove vs. Kathy Kuykendall.

In the upper quarter of the round of 16. Evert plays Nancy Richey (who is 5-5 with her lifetime, but now past her prime), and King plays No. 9 seed Kerry Reid.

Austin's victory stole attention from the medical reports on the top two men's seeds, Bjorn Borg and Jimmy Connors, who both won stadium matches easily - Wimbledon champ Borg over New Zealander Onny Parun, 6-1, 6-3, and defender Connors over Zan Guorry, 6-1, 6-4.

Borg, who strained a muscle underneath his right shoulder water-skiing and aggravated it in practice the day before the tournament began, still was punching his serves, but he thumped his topspin ground strokes with customary fury.

Numerous times he slugged deep forehand approaches and went to the net; Parun was as incapable of passing him as he was of winning backcourt rallies, and he curiously did not test Borg's much celebrated injury by lobbing.

"I know there is no way I can win any points on my serve, so that is bothering me. I have to work extra hard on my ground strokes," said Borg. "It will be tougher and tougher each round. Against (Dick) Stockton (his next opponent, winner of a magnificent match over Adriano Panatta, 2-6, 6-4, 6-4, Saturday night), I may be have to serve better, or he will attack and come in."

Asked if he could win the tournament if his shoulder does not improve, Borg said: "No way . . . not even a 1 per cent chance."

But his colleagues are getting tired of Borg's persistent moaning.

"He made the same comment at Wimbledon in 1976, and he served 11 aces in the final," said Vitas Gerulaitis, the No. 8 seed who plays Harold Solomon of Silver Spring, on Monday.

"If I come out here and lose, I'd love to think of an excuse, but you play and do your best. I've played plenty of times with injuries, and you can't make excuses.

"So big deal, Connors has a sore back, but I see him out there hitting the ball a thousand miles an hour. If I lose, I'm not going to say I had a sore elbow or didn't get enough sleep the night before or got bad calls.

"I'm sure they're all hurt, but I think everybody would be a lot better off if they just kept it to themselves," Gerulaitis concluded. "Every tournament that Connors has won he's been hurt, so he must be the best hurt player in the world."

Connors, who has not dwelled on his strained back, but was nevertheless testy after the match, next plays the Gerulaitis-Solomon winner if he gets past Stockton, he is in a tough quarter of the draw; the winner of his match with Tanner plays either 1975 champ Manuel Orantes or the winner of tonight's late match between No. 9 seed Eddie Dibbs and John McEnroe.

The other quarters are easier: No. 4 seed Guillermo Vilas vs. Jose Higuereas, to play John Feaver or Ray Moore; and Corrado Barazzutti vs. Butch Walts, toface No. 15 Wojtek Fibak or Brian Gottfried, a 6-4, 6-3 winner over Jan Kodes today.