At 23, Jill Sterkel is the 'grande dame' of US swim team

''Not long ago, the thought of a 23-year-old swimming in the Olympics would have been a joke.'' Jill Sterkel's words are entirely serious. A freestyler and University of Texas senior, she won a berth on the United States Olympic team in a sport where most competitors are teen-agers. The kicker is that Sterkel has been on two other US Olympic teams - in 1976 and '80.

As the grande dame of this year's team, and with a knowledge of the sport founded upon years of experience in the water and as a coach, the veteran competitor from Hacienda Heights, Calif., knows the ropes as well as anyone else. Her younger teammates recognize her leadership: Even though Jill herself probably won't win any medals this year, her presence in the role of mentor has been a significant factor in the team's overall development.

Only one other American female swimmer, backstroker Eleanor Holm, ever had enough staying power to make three Olympic teams. A veteran of the 1928 and 1932 squads, she was booted off the 1936 team for drinking on the boat over to Germany. Sterkel missed one of her three meets when the US boycotted the 1980 Olympics in Moscow.

The high-water mark of Sterkel's long career was that moment eight years ago at Montreal, where she won a gold medal in the 4 x 100 freestyle relay - the same event in which she will swim this time.

Sterkel, whose oversize-frame glasses give her a scholarly look outside the pool, recalls her naivete upon entering those games. ''I was 15 and everything was fun,'' she says now. ''I didn't seem to realize it was the Olympics or how good the East Germans were.''

That year, however, East Germany dominated the women's swimming events, winning every race up to the last. Sterkel, competing individually, finished seventh in the 100-meter freestyle and just failed to make the final in the 200. Eventually the entire US women's team - a group accustomed to carting off plenty of gold - was on the verge of being shut out.

''We had some people on the team doing personal bests, but it was definitely noticeable that we were getting embarrassed,'' she remembers.

Sensing that time was running out, the relay members met to map out a winning strategy. ''We sat down and worked out our times - Wendy Boglioli, Kim Peyton, Shirley Babashoff, and myself. It was a real team effort, just a neat thing,'' she says.

When Sterkel dived in to swim the third leg, the US was still slightly behind. ''The whole way down I wasn't looking; I think my eyes were closed,'' she recalls. ''When I pushed off on the turn, I saw the East German girl right there, and I just got my legs humming.''

Giving it everything she had the rest of the way, she propelled her team into the lead - and anchor woman Babashoff held onto it for a victory that triggered a memorable tear-filled celebration.

This year, Sterkel fell short in her effort to land an individual freestyle slot. By finishing sixth in the 100 meters at the trials, however, she earned an alternate's spot on the 4 x 100 freestyle relay team, which means she will swim in the preliminary heat of this event Tuesday morning, though probably not in the final later the same day. Only those who swim in the final are eligible for medals.

''I was relieved to make the team, but rather frustrated not to win the 100, '' she says. ''I wanted to go out in style. I felt I did everything I needed to do in preparation for the trials. Things just didn't work out. I can't explain what happened.''

In the eight years between her two Olympic appearances, however, a lot has happened to change women's swimming. The US women bounced back to achieve parity with the East Germans for a while, only to see their arch rivals, who are boycotting these Olympics, spurt ahead again.

But the Americans have stayed right in the picture, and now have an Olympic squad with a greater mixture of ages than ever before. This year sees the return of a number of '80 Olympic team members who lost their chance because of the Moscow boycott, including Tracy Caulkins and Nancy Hogshead (both of whom won gold medals Sunday as the swimming competition began), and Sippy Woodhead, Mary Meagher, and Kim Linehan.

What has made the difference, many feel, is the advent of swimming scholarships for women - who now compete straight through college rather than dropping out after high school.

Sterkel herself, for example, led the University of Texas to the 1981 and '82 national titles. In 1981 the strapping, 5 ft., 11 in. coed won the Broderick Cup as the nation's outstanding female collegiate athlete.

A student assistant coach at Texas this past year, she expects to graduate with a physical education degree next December, then possibly stay on as a full-time Longhorn assistant coach.

Meanwhile, when not swimming herself, Jill is serving as a sort of unofficial mentor here. She's happy to share her experience with her teammates, too, but one thing she doesn't think they need is any sort of pep talk. ''When you get waxed the way we did in '76, you learn how much you want it,'' she says. ''And I think we're at the stage right now where we really want it.''

It's obvious she feels the talent is there: When asked if she would attempt to inspire her teammates by showing them the '76 medal she won, Jill's succinct reply is, ''No, they'll get one of their own.''