When you're on vacation this summer, it may be difficult to carry your cello along. Or your piano, or your tuba. But a harmonica fits right in your pocket. Oh, sure, you say, but I can't play the darn thing.

Hold on, there -- you can. Meet Al Zankman, who has patented a method for learning to play the harmonica. Zankman believes that almost anyone can play the small, shiny instrument. He has taught 8-, 9-, and 10-year-olds in the classroom of his wife, who is an elementary school teacher, and says that in Japan, children learn the instrument in school the way many American youngsters learn the recorder, a relative of the clarinet.

"Older people find it's a revelation -- you can carry it around in your purse or pocket", he says. He knows too that many harmonicas are buried in drawers simply because people don't know how to play them.

Hence, the Z-Bird Harmon-A-Kit: a 10-hole German-made Hohner harmonica (Zankman says that Hohner is the world's largest harmonica maker) in the key of C, packaged in a small box; both recorded and printed instructions; a 9-inch plastic card holder and 10 rectangular cards with a song on each side. Insert one end of the plastic holder into the harmonica and affix the card of your choice to the other.

Following the instructions to draw in or blow out at the numbered holes, you'll find yourself playing the song on the first try. When you master the learning cards, you can buy special harmonica sheet music in music stores.

Z-Bird Harmon-A-Kit. $19.95, includes shipping and tax. Zanco Enterprises, Box 792, McLean, Va. 22101. 356-8184. Allow two to four weeks.