World Championship-bound Betsy Rapp, 18, and her sister Jenny, 15, qualified yesterday for the final in the women's 200-meter butterfly during the fourth day of competition at the AAU National Swimming Championships.

Jenny Rapp qualified fifth at 2 minutes 15.133 seconds with Betsy Rapp right behind in 2:15.21. They compete for the Starlit Aquatic Club in Fairfax, Va.

The top two finishers in each event here qualify for the World Championships Aug. 18-28 in West Berlin. Betsy Rapp was second in the 100-meter butterfly final.

A dual meet with Canada is slated for Aug. 22-23 at the Olympic pool in Montreal with U.S. members selected from the finalists at this meet. Beth Harrell of Alexandria, Va., was picked to compete in that meet after finishing sixth in the 100-meter butterfly Thursday.

Harrell is representing Solotar Swim Team, but trained this summer with the El Monte Swim Team in Los Angeles.

Melissa Belote of the DeAnza Swim Club of Cupertino, Calif., a former Solotar swimmer, was seeded sixth for last night's finals in the 200oter backstroke. Belote recorded a 2:18.83 in yesterday morning's qualifying, paced by Santa Clara's Linda Jezek, who qualified first in 2:15.78.

Jezek holds the American record of 2:15.22.

Other events slated for last night were the men's 200-meter backstroke and 200-meter butterfly. Today is the final of competition.