WASHINGTON, Feb. 5 — President Bush's plan for cars running on clean, efficient hydrogen fuel cells is decades away from commercial reality, according to a report by the National Academy of Sciences. Promoting the technology in his State of the Union address a year ago, Mr. Bush said a hydrogen car might be available as the first vehicle for a child born in 2003. On Monday, the Energy Department included $318 million for both fuel cells and hydrogen production in its 2005 budget. "Hydrogen is the next frontier; a hydrogen economy is where the world is headed," said Spencer Abraham,...