Next best to having these stories told aloud is having William Mayne tell about them--familiarly, appreciatively, probingly (and briefly). Also about their authors: ""Charlotte Hough is a good hand at this sort of story"" (""Angus"" from Red Biddy); Joseph Jacobs (represented here by ""Jack the Giant Killer"" and ""Jack and the Beanstalk"") ""knew that Britain had just as many stories as other European countries, and he thought that the Brothers Grimm. . . ought to be kept in their place""; or, best of all, Eleanor Farjeon--a tribute that should send children scurrying to The Little Bookroom from which ""The Giant and the Mite"" is taken. The galaxy of giants ranges from Greek and Norse mythology (Hawthorne's ""Three Golden Apples,"" ""How Loki Outwitted a Giant"" in the Picard version) to a selection from Gulliver's Travels and Oscar Wilde's ""Selfish Giant."" Folk tales from Amabel Williams-Ellis' British collection, Seumas MacManus' Bold Heroes of Hungry Hill and Sorche Nic Leodhas' Gaelic Ghosts are included also. Most, indeed, are readily available-although one of the most eloquent--Charles Molin's South American quasi-legend of a volcano entrapped--is not. But it's the quality and the alignment of the selections that counts here, and of course the introductions. Mr. Mayne is philosopical about giants and astute about stories.