Recent breakthroughs in hydrogen fuel-cell technology offer new hope that the United States could one day end its dependence on fossil fuels. Proponents of renewable fuels say non-polluting hydrogen could not only help end U.S. reliance on Middle Eastern oil but also dramatically reduce air pollution and emissions of carbon dioxide, the main greenhouse gas linked to global warming. The Bush administration is intensifying its support for fuel cells, including a proposal to spend $1.2 billion on hydrogen research over the next five years. But even critics who foresee a major role for hydrogen fuel cells note the administration is also proposing to increase domestic production of highly polluting fossil fuels, both to generate electricity and power cars as well as to produce hydrogen itself. Critics also say the administration is continuing to reject caps on carbon emissions and underfund subsidies for wind power and other renewable-energy technologies.