CLASSICAL Ravel, Maurice: ''L'Enfant et les sortileges.'' Susan Davenny Wyner, soprano, and other soloists. Ambrosian Opera Chorus, London Symphony Orchestra, Andre Previn, conductor. (Angel digital DS-37869) - Ravel's setting of Colette's little play is as enchanting a one-act opera as ever was written. Ravel magically captured the odd mix of fantasy and phantasmagoria, of innocence and wisdom. It is supremely difficult to stage: Making a room spring into action with singing sofas, dancing teacups, and an angry mob of small animals tests the imagination and skill of any director to the utmost. Perhaps the recording medium is the ideal way to present this, for even filmed attempts do not aurally capture the flavor of the work. Previn leads a sane, slightly whimsical, superbly played performance that allows the listener to hear every detail of Ravel's brilliant orchestration. Unfortunately, Susan Davenny Wyner, as the boy whose misbehaviors set this story into motion, is in poor voice, and this mars somewhat the vocal contributions to the opera. The large cast performs well enough, though without the distinction and sheer elan of those accumulated on the Lorin Maazel recording of the work on Deutsche Grammophon (138675).