Back and forth, back and forth at the base line, Kathy Jordan swayed, a pendulum in perfect rhythm. Always before in a contest of wills, when the match hung in the balance, the pendulum swung Chris Evert Lloyd's way.

But the laws of nature and expectation were violated today. Evert lost in the third round of Wimbledon, the first time in her career that she failed to reach the semifinals of a Grand Slam event, the first time since 1979 that she lost to someone not ranked among the top 10. The score was 6-1, 7-6 (7-2).

The loss also ended Evert's hope this year of joining Maureen Connolly (1953) and Margaret Smith Court (1970) as the only women to win the Grand Slam. Evert had won the U.S. Open and Australian Open in 1982 and the French Open last month.

When it was over, Jordan, who had a right to exult, was purposely subdued. "I don't think I knew what to do," she said. "I have a lot of respect for Chris. I won the match. What more could I do?"

In the women's locker room, there was shock and perhaps a bit of the lump in the throat that everyone at Court 1 shared. "We were all thinking that, somehow, she'll dig deep enough inside herself," said Billie Jean King. "But some days, no matter how deep you're digging, it's not enough."

"Nobody thought she could lose because she never lost," said Rosie Casals.

It was a strange day at Wimbledon. "Gray outside and Chris lost," said King.

Strange in the contrasts it offered, too. On Court 2, King and Casals played a match for memory. "Is that a relation of Rosemary Casals?" asked Michael Franklin, a club steward sitting in the stands. Informed that it was Casals, he said, "Good lord, is she still at it?"

They played tennis the way it was, even if it wasn't exactly the way they were. They served and volleyed and King, who is 39, did it better than Casals, who is 34, beating her for the 30th time in their professional careers, 6-3, 6-4.

King, who might have played Evert, her doubles partner, in the semifinals, now meets Wendy Turnbull. Although she says it would be a miracle for her to reach the final, stranger things have happened, as was evidenced today.

From the base lines of Centre Court, Carling Bassett, 15, and Andrea Temesvari, 17, slugged it out for the future of women's tennis. Bassett, who is ranked 28th and is a member of the Carling brewing family, won 6-3, 7-6 (7-2), after squandering six match points. "We knew the cutie-pies would be on Centre Court," King said.

Overshadowed on this overcast day was Jimmy Connors' impressive victory over Henrik Sundstrom, a young Swede, 6-1, 7-6 (11-9), 6-2. Sundstrom had three set points in the tie breaker and lost them, one when a called ace was overruled by the umpire.

Evert, who had reached the semifinals in 34 consecutive Grand Slam events, never looked quite right today. Her passing shots lacked precision. She had trouble with Jordan's big first serve, crisp volleys and slicing backhand, which skidded in lower and lower on the quick Court 1 grass. She said she thought Jordan had never played better.

Evert refused to make excuses for her play or her pallid appearance. "I wouldn't have walked out on the court if I didn't think I was fit," she said. But as her press conference ended, she bolted from the room, saying she had to leave. Officials later said she had been sick during the night with a stomach flu and had seen a doctor around 2 a.m. She took glucose during the match. Last fall, Evert won the U.S. Open despite a case of food poisoning resulting from cheesecake.

Jordan, who is ranked 26th, had never beaten Evert before, never taken a set from her before, never won anything before but one tournament, although she has won all the Grand Slam events in doubles. Jordan looked strong from the beginning. She broke in the first game of the match, after Evert had led, 30-0, a hint that Evert's resolve wasn't there.

Evert had break points in the second and fourth games but couldn't capitalize on them, a pattern that repeated all day. The only time she held serve in the set, she won the game on a let cord.

"If I lose a first set, I use it as a warmup," Evert said. "I have to think that way because I don't want to think, 'One more set and I lose the match.' "

But Jordan began the first game of the second set with an ace, and took a 40-0 lead. Evert rocketed a forehand return of serve down the line: an Evert return, fighting back to break. She won the next three games to lead, 4-0, looking increasingly like herself. Her lobs were better, longer, more effective.

Jordan consoled herself, told herself just to win a couple of games, get back in the set, so she wouldn't have to go into the third having lost, 6-0. Last fall, after the Open, Jordan took six weeks off to heal her aching shoulder, work with a new coach (Robert Landsdorp) and consider her attitude. She has been known to let her temper get the best of her and her game. Last week at Eastbourne, she lost to Virgina Wade. "I didn't play well and I misbehaved," she said. "I told myself, 'You have to have a good attitude or you might as well quit playing tennis.' "

Today, she just knew she would do well. Down, 4-0, she kept attacking, won two games, breaking in the sixth to make it 4-2. Then, she served the game of the match. Three times, Evert had break points and three times she lost them.

Jordan asserted herself, breaking in the 10th game at love. Evert stood at the base line, examining her racket and the dwindling possibilities. Jordan broke on the first point of the tie breaker with a forehand approach winner, took a 2-0 lead with a forehand winner down the line, and went to 3-0 when Evert's forehand lob sailed long. Evert reached up and touched her brow.

She knew. "I thought it would be tough to win the match," she said. "In the past, it's true, my opponents might get intimidated in a winning situation and Kathy played really well even when she was winning."

The scariest thing, Jordan said, is not the thought of winning: "You're more scared of getting to the chance of beating her and losing it."

She didn't. All week, people talked about a two-woman tournament, a show-down between Evert and Martina Navratilova. "They have such an aura of invincibility, I think it's better for the rest of us, better for women's tennis, to beat one of them," Jordan said.

Evert didn't have to explain her disappointment. "I don't think it matters whether she wins the Grand Slam or not," Jordan said. "She's always going to be remembered as a great champion."

As King said, "Three out of four ain't bad."

For Jordan, this was a first. Around her neck, she wore a necklace that said, "Sweetie." Sweetest, it should have said.