The head of the Environmental Protection Agency said Tuesday a finding that greenhouse gases such as carbon dioxide are a public-health danger won’t necessarily lead to government regulation of emissions, an apparent about-face for the Obama administration. The new position follows revelation of a White House document that warns the EPA of the wide-ranging—and potentially economically harmful—consequences of an agency finding last month that proposes declaring greenhouse gases are a danger to the public. The White House memo also undermines the EPA’s reasoning for the “endangerment” proposal. EPA Administrator Lisa Jackson has previously said such a decision “will indeed trigger the beginning of regulation of CO2.” But speaking before the Senate Environment and Public Works Committee, Ms. Jackson said Tuesday that an endangerment finding, “does not mean regulation.”