Make way for another distinctive musical hybrid: Jewish-American. The imaginative blend of old-time Jewish folk music (Klezmer) with bluegrass and country-western styles had its origins 11 years ago when two Washingtonians found themselves jamming in a bluegrass festival parking lot band to the traditional Pesach song "Dayenu."

Fiddler and mandolinist Alan Oresky of Silver Spring and guitarist David Shneyer already knew each other through folk Rabbi Shlomo Carlebach. Shneyer had come to Washington from New Jersey to join Fabrangen, an alternative Jewish cultural community (the name is based on the Yiddish for "coming together"). He and Oresky, a veteran of the old-timey band Fast Flying Vestibule, first met at a Carlebach concert in 1970. They've been inseparable since then as two-fifths of the Fabrangen Fiddlers.

"Alan's fiddle is the key to our sound," says Shneyer, who proudly points out that no other Jewish-American folk group offers the mixture or diversity of the Fiddlers, who also include pianist-singer Sue Roemer, clarinetist Frank Sparber and bassist-sitarist Theo Stone. Fiddlers? "Well, some of us do fiddle around on our instruments," Shneyer explains. He also points out that traditionally Jews in the Diaspora have adopted cultural forms from surrounding cultures while infusing them with Jewish themes and messages.

"Rhythmically the nature of bluegrass is very similar to Chassidic music, the principal change being going from major keys (bluegrass) to minor keys (Chassidic)," Shneyer says. "There's a similar intensity, a bit less serious and more joyful in bluegrass perhaps. It has a lot to do with the seriousness of the music's keys." The Fiddlers mix Hebrew, Yiddish and Ladino lyrics with bluegrass, traditional jazz and folk melodies, and in recent years have moved to a greater emphasis on the old-time freilach (happy) Chassidic swing-style in which the clarinet has "the ability to not only wail, but to laugh and cry as well." Says Shneyer, "Luckily, we can adapt instrumentally and stylistically to many different times."

The Fabrangen Fiddlers, who tour extensively and have recorded several albums, will perform tomorrow at 1 p.m. at the Museum of American History's pendulum area as part of the Smithsonian's free annual holiday celebration. They are one of several dozen musical organizations participating in the offering of concerts, films and crafts demonstrations from noon to 4 p.m. daily through Wednesday. For further information call 357-2700.