Herman J. Van der Linde, chief assistant public defender of Rockland County and a former New York City lieutenant of detectives, died yesterday at his home in West Nyack, New York. He was 58 years old. Mr. Van der Linde, who studied law at Fordham University, retired from the Police Department eight years ago. He was chief assistant district attorney of Rockland County before his appointment as a public defender. Surviving are his wife, the former Kathryn Hill; two sons, James and Gerard; a daughter, Kathryn: his father, a brother, and nine grandchildren.