New Yorkers had their first chance to hear the impassioned singing and heady rhythms of rai - West Algerian rock - when Cheb Mami performed Tuesday night at S.O.B.'s. Rai arose in Oran, a port city, when musicians adapted traditional melodies to electronic instruments while letting in some Western musical influences. Song lyrics, in Arabic, often speak of forbidden love or assert the singer's independence, addressing a younger generation that is ambivalent about traditional ways. Rai singers call themselves ''cheb'' (or ''chaba'' for women), which means ''young''; Cheb Mami is 23 years old.

Cheb Mami's music balances with graceful tension between old and new, and is extremely popular in Algeria and France. His band uses electric guitar and bass, keyboards and trap drums along with violin (long adapted to Middle Eastern music) and the darbuka, a hand drum.

To a Western ear, the songs seem exotic. They use sustained introductions akin to traditional music, and the rhythms roll briskly instead of defining a Western backbeat; a few chords carry Cheb Mami's grainy, urgent, minutely ornamented vocals. The band also uses Western touches - its keyboard or violin often play melodic hooks, while one song's loping rhythm suggested Algerian-accented ska - but the music is just barely internationalized, and is stronger for it.

The early set took off about halfway through, with a song propelled by rapid-fire darbuka drumming. But because so few people were dancing, Cheb Mami cut most songs a little too short, not giving the music time to sweep listeners away.