The European Union and the U.S. agreed yesterday to team up on research into hydrogen fuel cells, widely touted as a potentially clean power source that will revolutionize future energy use. But while the E.U. wants to develop hydrogen using renewable energy sources such as solar and wind, the U.S. has plans to use fossil fuels and nuclear energy to power a hydrogen revolution. Some critics charge that the E.U. is letting the U.S. hijack its hydrogen agenda. U.S. Energy Secretary Spencer Abraham, speaking yesterday in Brussels, Belgium, sought to reassure European officials that the U.S. is committed to developing hydrogen from a wide range of sources, including renewables. He said half of the $1.7 billion that the Bush administration has pledged for hydrogen research will go to projects involving renewables. But Jeremy Rifkin, who is advising E.U. leaders on hydrogen issues, characterized the Bush administration’s hydrogen initiative as “a Trojan horse” for the nuclear and fossil-fuel industries.