Suspended Newton Police Chief Matthew Cummings plans to fight accusations of unbecoming behavior and will ask that his dismissal hearing be held in public, his lawyer, Timothy M. Burke of Needham, said Thursday. Burke said Cummings disputes assertions that he made derogatory comments to Jeanne Sweeney Mooney, his former secretary, and two other women in the department. Mayor Setti Warren announced last week that he had placed Cummings on paid administrative leave and had started proceedings to fire him after a report indicated that the chief’s comments and behavior could be perceived as offensive.