I am primarily interested in criminal law and my specialty is murder,"" says this two-fisted, blond, rhumbaing lawyer who has made a practice of defending those at the bottom of the urban refuse heap--mainly blacks and Hispanics accused of murder, rape, incest, mutilation, and armed robbery. Those whom the tabloid press calls ""animals."" Her own start in life--in an overcrowded, poor rabbi's family where Daddy alone was top dog--gave her the stubbornness to make it through law school and the bar exams. And so into the courtroom, where a particularly tormenting judge advised her to ""go home and cook chicken soup for your husband."" But though Halbert's feminist fervor is strong, most of this gutsy book is about her clients--whose cases she investigates, if need be, by traipsing through tenements and abandoned hovels to gather witnesses and evidence. To her, at least, the people she represents are often more piteous than monstrous: a mother confused by voodoo spirits, charged with murdering her baby; a man accused of killing his girl friend, innocent but afraid to testify because ""I. . . am dumb."" In one headline-making case, a man she represented had been incarcerated for four years as criminally insane because he swore--truthfully--that he had seen someone drink his own blood. Halbert doesn't flinch, though the reader might, and manages to inject her own fortitude and humor into the most gruesome tales. No wonder the prisoners say ""Never fear, Sara's here.