WASHINGTON  The Energy Department strives to be a leader in championing energy efficiency. Its Web site lists energy-saving tips, while Secretary Steven Chu calls conservation one of the department’s most important goals.

But at many of the agency’s buildings, even at national laboratories where talented scientists seek technological breakthroughs to save energy, the department has failed to use one of the most effective tools available to any ordinary household: thermostats that automatically dial back the temperature when nobody is around.

A recent audit found that the department could save more than $11.5 million annually in energy costs by properly employing these “setback” controls to adjust the heat and air conditioning at night or on weekends.

The Energy Department’s inspector general found that the department, which spends almost $300 million annually on utilities, could save enough energy to power more than 9,800 homes each year by doing what experts say every household in the country should also be doing.