Former Secretary of Defense William Perry, now a Stanford University professor emeritus of management science and engineering, lists biomass, plug-in hybrid cars, nuclear power, more natural gas and energy efficiency as the only potential near-term answers to easing the United States' emissions of greenhouse gases and addiction to oil.

Of these items, what is the most important?

"I would put energy efficiency as No. 1 on my list," Perry said recently at a Stanford conference. "We should redouble our efforts." Biomass and hybrid cars are still developing, he said, and nuclear power faces too much public resistance, at least in the United States.

Perry said that wiser energy use holds advantages for the economy, as well as for the environment and security. For example, two-thirds of the U.S. trade deficit is due to oil imports, but stricter mileage standards could reduce prices and imports.

Perhaps surprisingly, Perry is not the only former military chief pressing for greater energy efficiency. At the same meeting, Robert M. Hill, Australia's former minister of defense, described his country's renewed attempts to cut waste. The Low Carbon Australia trust, which finances efficiency improvements in private buildings with public funds, is chaired by Hill, a member of Australia's main conservative party and a professor at the University of Sydney.

"It's quite criminal how much energy we waste," Hill said at the U.S.-Australia Dialogue on Energy Efficiency conference, organized by Stanford's Precourt Energy Efficiency Center (PEEC) and the government of Australia through its consulate in Los Angeles.

Despite the potential benefits to the environment, economy and national security, most governments have not acted decisively to reduce energy waste. "Visionary statements" have been followed up by little real action, said Howard Bamsey, a professor of climate change and energy security at the University of Sydney's U.S. Studies Centre.