by Romain Gary. World, $6.95. Mr. Gary’s ironic story of the dog trained to attack blacks on sight is presumably true, for it involves well-known people (there is a tartly funny sketch of Marlon Brando up to good works) and actual events— although the dog never impinges on any of them. True or not, the tale serves as an excuse for Mr. Gary’s comments on racial affairs in this country, a matter on which he is somewhat less pessimistic than the natives and a good deal more sensible.