Beethoven and Debussy are remarkably compatible compowers. Each reflects strong ties to a linguistic idiom, and unabashed expression of personality and a wrestling with structural forms. That their manners of expression are so different but so satisfying, that their solutions to similar musical problems are so different but so elegent, makes the juxtaposition of their music on the same program particularly effective.

Last night at the Renwick Gallery, the Emerson String Quartet, with the assistance of pianist Lambert, Orkis and soprano Lucy Shelton, devoted the first half of its concert to Beethoven and the rest to Debussy. The programming and the performances collaborated in making this a particularly pleasant occasion.

Performances by this group are generally marked by a sense of genial and warm ensemble, by organically shaped phrases and by comfortably, unhurried pacing. All of this came together last night to produce a perfectly marvelous reading of the Debussy G Minord Quartet. The large cyclic structure asserted itself without being apparent. The instruments spoke in the most subtle French tone of voice, and throughout there was a reliable backbone of rhythmic strength.

Much the same kind of attention was lavished on the opening Beethoven Opusd 135 Quartet. But Beethoven, even in a retrospective piece like this, can use more directness than this performance provided.

To a delightful set of nine Beethhoven folksong settings and two of Debussy songs, Lucy Shelton gave the benefit of her accurate and intelligent singing. Her voice is more notable for its energy and life than for its subtlety, so the Beethoven fared better than the Debussy did, but both were unfailingly musical.