Timely profiles of political personalities suffer from legions of glaring disabilities, and certainly one would be extremely naive to expect them to be candid. Particularly is this so when the author -- as is the case here -- has served as a close assistant to his subject for several recent and critical years. With these facts in mind, it is safe to say that Mr. Griffith has done a very reasonable job, with considerably more frankness and less damaging bias than might well be expected. His admiration for Hubert Horatio Humphrey the man is sincere and unstrained; his advocacy of Humphrey ""the liberal and politician"" as future President is understandable even if not necessarily shared. The relative success of this effort is in large part due to the ""open"" character of the subject. ""He is a happy man,"" says the first sentence, and before very many pages, one believes it. The energy, impulsiveness and conviction come through quite irresistibly. Strict chronology and any attempt at being definitive are, wisely, ruled out. The emphasis is on the period (1960-64) when the author was a daily, first-hand observer, but interviews with persons who knew Humphrey as a young man, mayor or junior Senator are used to sketch in the necessary background. And, while every mention of a possible fault is promptly overbalanced by the citation of a greater virtue, the effects of a modicum of independence are in evidence.