The Obama administration is cracking down on doctors who repeatedly overcharge Medicare patients, and for the first time in more than 30 years the government may disclose how much is paid to individual doctors treating Medicare patients. Marilyn B. Tavenner, the administrator of the Centers for Medicare and Medicaid Services, said that ?recalcitrant providers? would face civil fines and could be expelled from Medicare and other federal health programs. In a directive that took effect on Jan. 15 but received little attention, Ms. Tavenner indicated that the agency was losing patience with habitual offenders. She ordered new steps to identify and punish such doctors.