KING OF THE NIGHT The Life of Johnny Carson <i> by Laurence Leamer (William Morrow: $19.95; 448 pp.) </i>

It’s no accident that the title “King of the Night” carries dark-side connotations. Laurence Leamer’s objective is to expose the seamy underbelly of the affable host of “The Tonight Show,” a man whose long-lived popularity defies all laws of the entertainment world. Leamer appears to have interviewed hundreds of Carson acquaintances, from Omaha to Hollywood. He goes to great length to gather unflattering evidence, and his credo seems to be: “No detail is too small if it reflects badly on Johnny Carson.” In the description of the 25th-anniversary celebration for the “Tonight Show” that begins the book, there’s a scene at the urinals on board the Queen Mary; moments later, Leamer does not neglect to report, Carson stiffs the attendant as he exits the men’s room.

One theme of Leamer’s narrative is the difference between Carson and other comics. Unlike the comedians whose routines he assiduously studied as a youngster--Jack Benny was a favorite--Carson sailed through the Depression and World War II without ever suffering hardship or horror. Carson’s business sense similarly is a point of scorn: “A good comedian can get you to buy his sponsor’s product,” Carson wrote in a college paper. Comments Leamer: “One could hardly imagine the youthful Charlie Chaplin envisioning a glorious day when the genius of his tramp would be used selling IBM computers.” Leamer carefully describes how Carson learned to create an illusion of daring while never putting himself on the line.

In covering Carson’s career, Leamer perforce gives an entertaining account of the rise of television. Much of the book, however, deals with Carson’s relations with women, the sordid nature of which Leamer traces to his relationship with his disapproving, sarcastic mother. Readers interested in capsule descriptions of messy affairs, loveless marriages and alcoholic escapades should look in the pages of current tabloids, where the book is getting big play. In short, “King of the Night” is celebrity deflation as much as celebrity biography.