Federal agencies will hold two public hearings this week on a proposal to designate Atlantic salmon populations in the Penobscot, Kennebec and Androscoggin rivers as endangered species. Atlantic salmon in eight smaller Maine rivers or streams already are protected under the federal Endangered Species Act. The current proposal would expand the protected population of Gulf of Maine salmon to include the state’s three largest rivers. The National Marine Fisheries Service and the U.S. Fish and Wildlife Service will accept public comments on the endangered species proposal, as well as a critical habitat proposal, on Wednesday night at the Augusta Civic Center and on Thursday night at Jeff’s Catering in Brewer. Federal biologists will hold informational sessions before both meetings from 6 to 7 p.m. Written comments can be submitted through Dec. 2 on expanding the endangered listing and through Dec. 5 on the Gulf of Maine critical habitat designation.