One of the busiest, most conscientious actors in Hollywood, Martin Sheen has put together a Herculean body of work, much of it forgettable, yet sifting through the chaff reveals a vast array of gem-like grains to beg his mention among the great actors of his generation. He became established playing youths run amok, and though the resume boasts its share of villains, he has grown over the years into a patriarchal figure, whose rectitude and social responsibility is in keeping with his very liberal Catholic activism. The proud family man has seen all four children enter the acting business,