CHAPEL HILL, N.C., JULY 14 -- Since 1982, swimming officials have utilized the Olympic Festival as a proving ground for the nation's junior swimmers. This year they still kept the average age under 18 but upped the ante, making a high finish in the national championships the deciding factor.

They were predicting that the meet records, most of which were set five years ago, would fall quickly and Sarah Anderson, 17, of Moreno Valley, Calif., took it to heart, setting the only individual record of the first day of swimming, in the 200-meter freestyle.

At the close of the meet, the North 800-meter freestyle relay team of Anderson, Sheri Smith, who was second to Anderson in the 200; Nadine Takai, winner of the 400-meter individual medley, and Annapolis' Mary Petry, who took fourth in the 100 butterfly, set a meet record of 8:22.03. The South team swam 8:22.76 last year to set the former mark.

In the women's open 200 tonight, Anderson was fourth at the first 50 meters, moving into first with 100 meters left and held on to a three-tenths of a second lead over Smith to win in 2:03.67. Her best time by three seconds, it knocked half a second off the former mark, 2:04.12, set by Mary Wayte in 1981.

"I swam it exactly the way I wanted to," said Anderson, who has been stuck on a plateau with her 200-meter times the last two years. "I knew a drop was coming,"

She will swim the 800 meters Wednesday and the 400 meters Thursday.

This meet is scheduled two weeks before the long course national championships, which is the major focus for the swimmers here, most of whom participated in their first or second nationals to qualify for this meet. Much has been made of that fact and officials have been saying all week that the swimmers would not be at their peak. Nonetheless personal bests were the order of the day even if records weren't.

"It could be the pool," said men's 400-meter freestyle champion Steve Herron, 17, of Kirkland, Wash. "It's a fast pool." He cut 1 1/2 seconds off his previous best with a 4:02.75, something he hasn't been able to do for two years.

The Koury Natatorium, opened last fall, is technically advanced and designed to produce fast times. This is its first use in a major competition, the first opportunity to test the effectiveness off the deeper bottom, new wave-absorbing lane ropes and wide gutter lanes.

Three Washington area swimmers were among the eight scoring finalists in two events.

For Bryan Nicosia of Ashton, Md., and the Curl Swim Club, who finished fourth in the 100-meter breaststroke (1:07.37), this meet presented the opportunity to work on a recently altered stroke before the nationals. He was fourth in the World Championships trials last year.

"This was more of an indicator swim for me," he said. "There are still a lot more things I have to do with my stroke and if I wasn't here I couldn't be working on it in competition."

Susan Leupold of Arlington and Curl and Petry, 13, the youngest swimmer here, both competed in the 100-meter butterfly. Petry finished fourth (1:03.17) and Leupold was eighth (1:03.43), both best times.

Nicosia will swim the 200 breaststroke and Leupold and Petry both will compete in the 200 butterfly Wednesday.

In addition to the pool, the swimmers here were testing the theorized positive effects of altitude training. Eight swimmers trained in Colorado Springs while a control group trained in Florida. Five of the altitude group swam today.

Chas Morton of Franklin, Tenn., won the 200-meter individual medley; Mike Johnson of Ankeny, Iowa, took fifth in the 400 freestyle; Rosie Zimsen of Bremerton, Wash. finished 10th in the 100 butterfly; Laura Gandrud, a sprinter from Edina, Minn., far exceeded expectations to finish fifth in the 400 individual medley, and Jodi Quas of Joliet, Ill., took sixth in the 100 backstroke.

While tickets for men's basketball, traditionally one of the most popular venues at the Festival, are still available, all three days of swimming are sold out. This evening's attendance of 1,733 was 500 more than capacity for the natatorium. Bleachers were added to accommodate the overflow.

The North team leads with 144 points. South is second at 121. East has 119 and West 97.

Finalized participants lists for volleyball and cycling were released today. Chris Kirkpatrick, 18, of Washington is on the men's East cycling team. Cycling competition will begin Thursday. Michelle Ja- worski of Potomac (South) and Scott Metcalf of Silver Spring (East) will begin volleyball play Saturday.

Marine Cpl. Craig Pittman of Quantico won both his opening matches of the best of three series and will face second seed Tom Erikson in the 286-pound weight class in freestyle wrestling Wednesday.

Pittman, the fourth seed, had to compete in the mini-tournament Monday to qualify for the freestyle tournament, unlike the top three seeds who qualified at the U.S. open earlier in the year.

Today he beat third seed Dean Hall, 5-4, in sudden death overtime and again by a score of 8-2 in the second match.