The EPA is expected to announce by the end of the week that it does not believe it has the authority under the Clean Air Act to regulate emissions of carbon dioxide and other greenhouse gases. This decision comes after the EPA issued rules making it easier for power plants and factories to upgrade without costly pollution controls. The decision is the administration's first legal response to lawsuits seeking to force regulation of greenhouse gas emissions, and environmentalists plan to sue the administration over its interpretation of the Clean Air Act. The outcome of this fight could affect various state-level efforts to cap greenhouse gas emissions.