The U.S. Olympic Track and Field Trials ended Saturday about the same way they began. Jackie Joyner-Kersee was giving further proof that she might be the modern Babe Didrikson. Her sister-in-law, Florence Griffith-Joyner, was knocking 'em dead in the sprints with her speed and her Fredericks-of-Hollywood body suits. Mary Slaney was proving that she's still unbeatable in her homeland, although for a moment she looked vulnerable.

On the men's side, there were more upsets to fuel the old argument over America's Trials-by-fire method of picking its Olympic Team. Say goodbye to Jim Spivey, and hello to Jeff Atkinson (who?), America's newest miling (and smiling) hope. While you're at it, say a sad goodbye to Greg Foster, who, world champion or not, couldn't carry a broken arm full of plates and screws over 10 hurdles fast enough to make the Olympic team. Not all of the old gang is gone, though. Mac Wilkins made his fourth Olympic team, at the age of 37.In all, some 21 meet records were set in the trials, not to mention two world records and three American records. Predictably, most of the record setting was in the sprints and hurdles; questions remain about America's international strength in the middle-distance and distance events. Nevertheless, the Olympic trials competition proved so strong that 16 medalists from the 1984 Olympic Games failed to make the team.

"Our team has been awesome," said Olympic head track coach Stan Huntsman earlier in the week. "I was sick coming home from Rome (the World Championships) last year. I am on a high right now. We've shown we won't be a pushover in Seoul."

Certainly not where the Joyners are concerned. As expected, Griffith-Joyner won the 200-meter dash, but didn't set a world record, as expected. She had to settle for a time of 21.85, after setting an American record of 21.77 in Friday's heats. Considering her astounding world record of 10.49 in the 100-meter dash a few days earlier, it wasn't a bad week.

In the Olympics, she said, "I want a world record in the 200. In the 100, I will just go for a win."

Wait till the gang in Seoul gets a load of this lady, who dresses like Cher Bono or a cocktail waitress, take your pick. She wore a black and white number with tiger striped bikini bottoms for the semifinals, then chucked them, as usual, for another number in the final - a white, lacy, see-through getup. "It's a negligee," she said. "A friend gave it to me and I promised her I'd wear it . . . Yeah, I hear the ooos and ahhhs and What is thats."

For the first time all week, Flo had company near the finish line. Pam Marshall was second in 21.93 and Gwen Torrence third in 22.02, leaving Olympic 200-meter gold medalist Valerie Brisco fourth.

Joyner-Kersee, who set a huge world record in the heptathlon to start the meet, was also chasing a record on Saturday but came up short. She won the competition with a leap of 24-5 1/2, which would have left her just inches short of the world record - except it was wind-aided. "I kept watching the wind gauge, and I thought it was legal when I went," said Joyner-Kersee, who made only one legal jump (of 21-0) after injuring her left knee on her third attempt. She beat her two nearest rivals, Sheila Echols and Carol Lewis, by nearly two feet.

Like Joyner-Griffth and Joyner-Kersee, Slaney is hard put to find competition in the U.S. and so she races the clock. She said she would try to break four minutes in Saturday's 1,500-meter final, and she also complained mildly that she rarely has anyone to run with in domestic meets. She got both of her wishes on Saturday. Regina Jacobs closed Slaney's 15-meter lead on the gun lap and trailed by a step entering the homestretch, but you-know-who prevailed. Slaney clocked a meet-record 3:58.92 - the third fastest ever by an American. Jacobs finished in 4:00.46 and Kim Gallagher 4:05.41.

"That was one of the better 1,500s that's been run in this country," she said.

The men's 1,500 was not. For 3 1/2 laps they plodded along, pushing and shoving in a tight pack until all heck broke loose on the final lap. In the end, somebody named Atkinson, a 25-year-old former Stanford student, had won, in a slowish 3:40.94. Steve Scott, who is easily America's top miler, along with Jim Spivey, was second in 3:41.12, but Spivey, the '87 World Championship bronze medalist, wasn't so fortunate. Mark Deady, another stranger who has yet even to achieve an Olympic qualifying time, edged him for third, 3:41.12 to 3:41.31.

"That was crazy; it was the roughest race I've been in," said Scott.

Spivey won't be the only proven performer to be left out of the Olympics. Foster, the two-time world champion and Olympic silver medalist, broke his left forearm two weeks ago - a break so severe that it required 12 screws to reassemble. Against doctor's, he competed in the trials anyway. He survived the first two rounds, but in the semifinals he hit the sixth hurdle. Fearing a fall, he stopped before the eighth hurdle and, holding his arm, calmly walked off the track to a standing ovation. He'll watch defending Olympic champion Roger Kingdom (13.21), Tonie Campbell (13.25) and Arthur Blake (13.28) represent the U.S. in Seoul.

"I'll take the rest of the summer off and start again next year," he said.

Wilkins has taken most of the last four years off since winning the silver medal in the last Olympics, but he was back again Saturday, wearing a Mac-is-back T-shirt. At 37, he wasn't the oldest in a final that included two men over 40, but he was the best. He threw 216-6 to best Mike Buncic and Randy Heisler. He'll be America's oldest track and field Olympian.

"My throws today make me a medal contender but not a gold medal contender," he said. But he proved that even at 37, he has more time.