In a sign of the increasing political importance of environmental issues, close to half of the U.S. Senate called on the Bush administration yesterday to postpone implementing proposed changes to the New Source Review rules under the Clean Air Act, pending a complete analysis of the potential impact on air quality and public health. A letter signed by 44 senators and directed to U.S. EPA Administrator Christine Todd Whitman noted “serious concerns that the changes could allow more air pollution — causing more asthma, more heart and lung problems, and more premature deaths.” The list of senators included three moderate Republicans and at least six Democrats involved in tight reelection campaigns. The New Source Review rules currently require utility owners to install state-of-the-art pollution-control equipment when upgrading power plants and refineries.