Researchers have confirmed that babies can ingest cocaine through a mother's breast milk, a Northwestern University pediatrician said. The study by Dr. Ira J. Chasnoff, published in the December issue of the Journal of Pediatrics, is being used by authorities to investigate the death of a baby in Detroit in which an 18-year-old mother nursed the baby after smoking crack, a pure form of cocaine. Chasnoff, chief of Northwestern's Perinatal Center for Chemical Dependence, said in Chicago that he was contacted by Wayne County, Mich., authorities because of his research. Chasnoff's study details the case of a 2-week-old Illinois infant girl whose mother was breast-feeding while she sniffed cocaine. The child became ill but after about 2 1/2 days, doctors were able to clear the cocaine from the child's urinary tract, the researchers said.