Washington ? The U.S. can reduce its dependence on foreign oil and greenhouse gas emissions by making cars and buildings much more energy efficient, according to a study released Tuesday by a national association of physicists.

The 46,000-member American Physical Society argues the need for action is urgent because the energy crisis is the worst in U.S. history. It also says the physics and chemistry behind the human causes of climate change – such as heat-trapping pollution from the burning of fossil fuels – is “well understood and beyond dispute.”

The report argues that the country can still go a long way to reduce energy use in cost-effective ways that allow for continued comfort and convenience. Although efficient energy technologies can save money, the U.S. has been slow to catch on, the report says. It recommends that the federal government adopt policies and make investments.

“The opportunities are huge and the costs are small,” the report said.

The report’s authors noted that both Republican John McCain and Democrat Barack Obama have called for improvements in energy efficiency and reduced oil imports and emissions. They said that the public also wants these changes because of worries about global warming, gasoline prices and national security.

“The bottom line is that the quickest way to do something about America’s use of energy is through energy efficiency,” said Burton Richter, the chairman of the study panel and a 1976 Nobel Prize winner in physics. “Energy that you don’t use is free. It’s not imported and it doesn’t emit any greenhouse gases. Most of the things we recommend don’t cost anything to the economy. The economy will save money.”

The report concludes that the projected growth of energy use in buildings – 30 percent by 2030 – could be cut to zero using existing technology and what’s likely to become available in the next decade at the current level of research and development. It argues that the federal government should encourage states to set standards for residential buildings and make sure they’re enforced.

“One of the things we would love to see is all buildings have Energy Star labels,” Richter said. “Right now you don’t know how much energy a building is going to use that you’re interested in moving into. We’d like to see an energy audit required before a building is sold or even built.”

Some of the report’s suggestions included installing roofs that reflect rather than absorb the sun’s energy in hot climates, more efficient heating, cooling, lighting and appliances, and more government investment in research and development in building technologies.

Consumers would have to pay to install the technology, but they would save money in the long run, the report said.

On transportation, a key recommendation is more federal government investment in developing cheaper and more reliable batteries for electric cars.

“If you look at magically converting the whole fleet to plug-in hybrids” that get 40 miles per charge, greenhouse gases would be reduced by 33 percent and gasoline use by 60 percent, Richter said.

That would be the equivalent of cutting oil imports by 6 million barrels a day, Richter said. That’s the amount the U.S. imports from OPEC (largely from Saudi Arabia, Venezuela and Nigeria), out of a total of about 13.5 million barrels imported a day from all countries.

“So if you’re looking at energy security issues, which is government’s business, if you’re looking at the overall economy, which also ought to be government’s business, to spend a bit more on research and development to hasten the day when you’re going to get all these benefits is a good thing to do,” Richter said.