Runa Laila, who made her North American debut Saturday night at the Kennedy Center in a concert sponsored by the U.S. Bangladesh Cultural Forum, is what movie fans on the Indian subcontinent call a "playback singer." That means she spends much of her time recording studios, singing songs for the southtrack of one film after another.

At 25, in fact, she has already recorded 3,000 songs in 10 languages, so when she asks her audience, which Saturday included both Chip Carter and a Mao-suited mini-delegation from the Chinese liaison office, for request, there's never a shortage of material. Her repertoire even includes Western numbers such as "Love Me With All Your Heart" and Joan Baez's "But Not Too Hard."

But what her Bangladeshi fan, the largest and most vociferous element in the crowd, seemed to want to hear most were well-known folk numbers and theme songs from favorite movies. Laila obliged them by singing tunes such as the traditional boatman's song "The Rivers Are Like the Tears That Flow From My Eyes" in a clear, ringing and controlled soprano.

The American bass player and violinist who was supposed to give this music a bit of rythnic punch was usually inaudible, but the rest if Laila's ensemble, four musicians associated with Radio Dacca, was splendid. Particularly impressive were flutist Abdur Rahman, who frequently echoed Laila's melodic trills on his wood instrument, and the two-man percussion section of Devabrata Chowdhury and Mohammad Sadeque Ali.