UNTIL recently, it wouldn't have occurred to me that gardening would be a popular pastime for the totalitarian set. But a droll little footnote in a recent biography of Josef Vissarionovich Djugashvili -- you can call him Stalin -- set me straight. Or perhaps I should say, it re-educated me. In ''Young Stalin,'' the author Simon Sebag Montefiore travels back to the wild streets of Tbilisi, Georgia, to uncover Stalin the gangster, the extortionist, the bank robber, the poet and the street operator. The biographer's bold ambition is to suggest how this cobbler's son and onetime seminarian could grow up to become perhaps the century's defining dictator. Oh, and incidentally, also an avid gardener. [ABSTRACT FROM PUBLISHER]