ANYBODY (well, almost anybody) can tap dance to Gershwin, and tap dancing is almost the only logical reaction to some of the music from "42nd Street." The National Tap Dance Company of Canada will be dancing up a storm to that kind of music in this week's National Symphony Orchestra pops programs, and will throw in for good measure a medley from Leroy Anderson, who also sounds eminently tap-danceable.

But this week's six skilled and highly energetic NSO guest artists will reach their peak only when the orchestra strikes up Bach's Third Brandenburg Concerto, and the dancers, seated in chairs, begin to tap their feet, clap their hands, wiggle and jump until they are clattering across the floor in patterns as graceful and intricate as those of Bach's music. There is nothing else in show business quite like these dance analogues of the Swingle Singers.

With the arrival of video recording, we have now reached a level of civilization in which the efforts of groups like this can be preserved and replayed in our homes as readily as those of the Juilliard Quartet. There is a lot of catching up still to be done in video recording, but the National Tap Dance Company of Canada's Brandenburg Concerto No. 3 has been taped and distributed by Video Arts International as part of a videotape titled "All That Bach: A Celebration." The tap dancers make up only about 10 percent of a 50-minute tape devoted to a survey of the wild and wonderful ways Bach's music is being used more than three centuries after his birth. But they are one of the most memorable segments in a very vivid program.

NATIONAL TAP DANCE COMPANY OF CANADA -- "All That Bach: A Celebration" (Video Arts International, Beta or VHS 69037). The company performs with the NSO at 8:30 Friday and Saturday in the Kennedy Center Concert Hall.