A veteran Quincy police captain has been charged with assaulting his estranged, pregnant wife. Michael J. Miller was arrested by Plymouth police Saturday on a charge of aggravated assault and battery. His attorney, Jack McGlone, said Monday that his client denies the allegations. Miller declined to comment as he left Plymouth District Court, where his arraignment was postponed until July 15. Quincy Police Chief Paul Keenan said that Miller is on paid administrative leave and that his gun license has been suspended. A police report said Miller’s wife told officers he hurt her Friday by opening her apartment door when he knew she was behind it. Police said that the Millers are separated and that Miller was there to pick up a child.