President Barack Obama said Thursday his administration's plans to invest heavily in energy research during the economic recession will create the types of jobs and technology the United States needs to remain the world's top economy. “I know it's not easy,” Obama told workers at an electric-car factory in Pomona, California. “There are days … when progress seems fleeting and days when it feels like you're making no progress at all. That's how it feels in the White House sometimes, too.” The U.S. president defended injecting billions of dollars into energy research, saying that revolutionary discoveries are often the result of deliberate effort over long periods of time. Obama's visit to the Los Angeles area was to promote the $787 billion economic stimulus plan and grow support for his $3.6 trillion federal budget proposal. Both emphasize “green” activities that use renewable energy or reduce U.S. dependence on oil imports. “Even as our American automakers are undergoing some painful adjustments, they are also retooling and remaking themselves into an industry that can compete and win,” Obama said. “Millions of jobs depend on it.”