IRON JOHN: A Book About Men by Robert Bly (Addison-Wesley: $18.95; 237 pp.). Less tough and introverted, more sensitive and thoughtful than their counterparts from the '50s and '60s, young men today would seem to have everything going for them. But while moderating encounter groups across the country, poet Robert Bly saw many break down into tears "within five minutes." In this sharp and sympathetic study of social identity, Bly traces the roots of that grief to a father-son rift that began when the Industrial Revolution placed sons in compulsory schools, leading them to view dad only through the critical eyes of their female teachers. As an alternative to the tarnished images of manhood that continue to pervade the culture (e.g., the CIA agent of the '60s or the TV dad of the '80s who "never knows what cold medicine to take"), Bly offers the model of the Wild Man. Unfortunately, while this "Zen priest . . . (who) resonates to hills, clouds and ocean" has inspired "gatherings" in woodsy locales from coast to coast, here he appears to be little more than a New Age superman, an image too idealized to help men make the difficult decision between trusting their primitive instincts and reining them in with the civilized mind.