THE SOVIET COLOSSUS: A HISTORY OF THE USSR by Michael Kort (Scribner's: $19.95). Michael Kort is no revisionist historian, and he breaks no new ground in his once-over-lightly treatment of the rise of the Soviet Union in "The Soviet Colossus." The Boston University teacher devotes fully one-third of his book to pre-revolutionary Russia on the generally accepted premise that a knowledge of the Soviet Union's czarist past is necessary to an understanding of what followed. The work deals mainly with internal Soviet developments since the Bolshevik Revolution, especially the power struggles within the Soviet Communist Party won by Josef Stalin after Lenin's death in 1924. Kort relates once again the horrors of the three decades of Stalin's rule that "resulted in the most murderous regime in human history." Kort concludes that although conditions have improved since Stalin's death, the way to get along in the Soviet Union is for the citizen to keep his mouth shut and do as he is told. The book is easy reading, and Kort does not burden the reader with the extensive use of source references. Also it carries the reader up to the initial period of the brief reign of Konstantin U. Chernenko, who died on March 10 after only 13 months as the Soviet leader.