Scientists involved in the program said that much of the discussion at the event centers on climate change. Many said they were surprised by the E.P.A.’s last-minute cancellation, particularly since the agency helps to fund the Narragansett Bay Estuary Program, which is hosting the conference. The scientists who have been barred from speaking contributed substantial material to a 400-page report to be issued on Monday.The move highlights widespread concern that the E.P.A. will silence government scientists from speaking publicly or conducting work on climate change. Scott Pruitt, the agency administrator, has said that he does not believe human-caused greenhouse gas emissions are primarily responsible for the warming of the planet.