Nonfiction briefly; The Stones of Venice, by John Ruskin.Edited by and with and introduction by Jan Morris. Boston: Little, Brown & Co. 239 pp. $29.95

''The Stones of Venice'' remains a pivotal work of criticism in the field of architecture and, possibly, as Ruskin would have wished, in all fields of art. Ruskin puts forth his theory on the interrelation of a people's architecture with their morality, using Venice for an example as the Renaissance reformed it.

However, quite remarkably, Ruskin's work has also become the definitive guidebook to Venice. As impatient as he was to alert his readers to his social and architectural theories, Ruskin never hurried through his descriptions of the Venetian palaces, displaying an uncommon appreciation for the smallest detail.

This newest edition has added several paintings of St. Mark's and the Ducal Palace to go along with the splendid sketches already included by the author, all of which provide a spectacular visual aid for Ruskin's colorful prose. Jan Morris's fine introduction supplies a glimpse into Ruskin's tormented personal life, showing how personal a work this book really is.

Perhaps Effie Gray, Ruskin's wife, spoke for all of us, reader and critic alike, when she said: ''John excites the liveliest astonishment . . . and I do not think they have made up their minds yet whether he is very mad or very wise.''