Villengen, West Germany — Page 1086 of the Villengen telephone book reads like a piece of history. Under the ''C'' section is the entry ''Caesar, Julius; Tyrant; 3 Brutus Street, Villengen (near Stuttgart). Tel. 84536.'' But dial the number and the call is intercepted by a recorded message (in German, not Latin): ''Disconnected.'' Telephone company officials, puzzled at how the entry got into the new book, are investigating. Mr. Caesar died in March of 44 BC.