Max Reger, the creator of forbiddingly difficult organ music, could also take a different tack. His ''Thirty Little Chorale Preludes'' are intended for semiprofessional organists always on the lookout for good organ chorales for use in Sunday church services. Reger selected the best-known tunes of his day from the Lutheran hymnal. Most of them are still in use today and form excellent additions to modern services. Michael Kube, in a detailed preface, draws a vivid picture of the composer and his superhuman creative powers.?