What would a Japanese rumba sound like? How about blues written by Johann Sebastian Bach?

Tap the right keys on Yaakov Kirschen's JFY music generator, and a computer will compose an original ditty in any of a variety of musical styles ranging from Druse Arab folk dance to bebop.Kirschen, a leading Israeli cartoonist who created the Jerusalem Post's "Dry Bones" cartoon, compares the process to breaking down music into basic genes that can be mixed and matched.

"We take pieces of musical DNA from different styles and tell the machine to recombine the pieces. What we get is an original piece of music," said Kirschen.

As he spoke, his fingers flashed across the keyboard to give a bongo beat to traditonal Japanese music. The result was, well, regrettable. Mixtures of classical and blues worked better.

With his machine, Kirschen says, he can mimic almost any style and produce, for example, the songs the Beatles might have written but never got around to.

The combinations are almost limitless, and about 27 million variations in the styles can be generated almost instantly.

The machine can also vary the instrumentation, changing from a clarinet to a trombone with a touch of the keys, and it can print out an instant score of music.

Such features are found in some commercial computers and music synthesizers.

But Kirschen, a 50-year-old immigrant from Brooklyn, N.Y., stresses that each computer tune from his music box is unique because it produces original songs, even though the tunes bear some similarities to their "parents."

He stressed that his machine did not store pieces of music, only a computer analysis of the style, the way notes and tempo were used.

"There is no song stored in here, only the relationships that the machine has found in the music," said Kirschen, who works in creative confusion around a bank of screens, sound boxes and half-eaten baigeleh, the Middle East version of bagels.

Kirschen, whose shock of untamed white hair gives him the appearance of a music conductor, developed the music generator in part because of frustration at being unable to make music.

"I can play 60 different instruments, all of them badly," he said, stumbling through "Oh Susannah" on the harmonica.

Using tunes he wrote on the JFY music generator, Kirschen registered as a member of the local musicians union as a composer.

Sally Ariel, general manager of Kirschen's LKP Ltd. in Jerusalem, said the firm is seeking a pioneer patent on the device. JFY Inc., a Long Beach, Calif., subsidiary, is marketing the invention, which costs about $25,000, to studios that make films, commercials and cartoons.

Users say it is a useful tool for making soundtracks because it can instantly invent a tune to match a mood and do it in any specified time period. It is also not temperamental.

"The machine's wife or husband didn't get up in the morning and create problems so a composer can't work. With a composer I have to make sure he's in the right mood to create. The machine always meets the deadline," said Dan Setton, a filmmaker of Set Productions Co. in Jerusalem.

Denis de Vallance, who runs a film production studio in Los Angeles, said he was using the machine to write background music for 26 films that need new soundtracks for marketing abroad and for animated films.

"A big part of pictures is the ambience. A lot of money and time goes into the background music, but in the end hardly anyone notices it," he said in a telephone interview. "This is a big time saver."

But he said there were many unanswered questions about copyright and that artificial music is likely to be as controversial as test-tube babies.