President Bush begins traveling the country today to win support for an energy proposal that calls for eliminating barriers to gas and coal power, opening up land to oil drilling and examining the use of a controversial type of nuclear reactor. The White House will call for $10 billion in tax credits to encourage the use of clean, alternate energy sources and to extend the life of aging nuclear power plants. And the Environmental Protection Agency will draft legislation to control air pollution, even as it considers rolling back existing clean-air rules.