Cynthia Woodhead set her second American record in two days during preliminary competition in the 200-yard freestyle yesterday at the AAU National Indoor Swimming Championships at the Texas Olympic Swimming Center.

The sixth American record of the meet came when Woodhead, 14, lowered Jill Sterkel's mark of 1:47.32 to 1:46.72. Woodhead, who swims for the Riverside (Calif.) Aquatics, set an American record Wednesday in the final of the 500-yard freestyle when she edged defending champion Jennifer Rooker.

Nashville Aquatic Club's Tracy Caulkins cruised through the preliminaries of the 400-yard individual medley in 4:18.49, only a little less than two seconds off her American standard, which should be in danger in the final.

Caulkins and Woodhead are the best examples of a new breed of female swimmer that is emerging in the United States. Caulkins is 15 years old and, although she is 5-foot-8, she weighs only 111 pounds. Woodhead also is a lightweight, weighing 109 pounds at 5-foot-4.

After the first night of competition, Starlit Aquatic Club of Fairfax, Va., was in seventh place in the women's events with 25 points, Solotar Swim Team of Silver Spring, Md., is the only other club from the Washington area to score women's points and is in 19th place with 12 points. Only Rockville, (Md.) Municipal Swim Center has scored points in the men's events with five and is in 22nd place.

Solotar has been hurt by the defection of two-time Olympian and triple-gold-medal winner Melissa Belote to a swim club in California.

Belote quit the Solotar team after six years and now is competing for the DeAnza Swim Club of Cupertino, Calif. Belote, 21, finished fourth Wednesday night in her specialty, the 200-yard backstroke, in her debut for DeAnza.

Belote said, "There are just not that many older kids to swim with in the Washington area. I also wanted to find someplace where I could concentrate on backstroke. Since the '72 Olympics, I have had to swim a lot of crazy events. I'm going to give it a try at DeAnza this summer and see if I have anything left."