Because he makes his work look easy, you're tempted to underestimate storyteller Jay O'Callahan. Listen to, say, ''Herman and Marguerite,'' which makes up half Earth Stories, a 50-minute album of five animal stories. O'Callahan's story sounds like a good radio play, with diverse characters and scenes of great humor and tenderness. But this is no play; this is one man, making his voice do amazing things. O'Callahan's work is a technical tour de force.
''Herman and Marguerite'' is miraculous in another way. This story is practically an epic, and it's about worms. Herman is an earthworm, Marguerite a caterpillar (''Dogerpillar?'' Herman asks, puzzled by this new species, when they meet). Over the course of the story, Marguerite not only turns into a butterfly but also has her life saved by an international chorus of worms. ''Herman and Marguerite'' is not Tristan and Isolde the relationship here is platonic, for one thing but it's a delight.
Earth's four other offerings include a Kiplingesque folk story, ''Hyena,'' and a couple of tender-young-boy-who-loves-animals tales. ''Frogs, Dodge City'' is a hilarious Western spoof whose climax involves a bunch of frogs singing and dancing on tabletops in a saloon where ''the sasparilly's flowin'.'' It's sort of a froggy Cheers. A