WASHINGTON— The Interior Department will make 16 million acres of public land rich in renewable energy resources available to the Defense Department, which plans to use the resources to reduce its reliance on fossil fuels, Interior Secretary Ken Salazar said Monday.

Defense Secretary Leon Panetta and Salazar signed a memorandum of understanding to encourage projects harnessing solar, wind, geothermal and biomass energy resources on public land, mainly in the Southwest, previously restricted for military uses.

The Pentagon said each service branch is expected to deploy 1 gigawatt of renewable energy  by the year 2025.

Under the Obama administration, some of the largest solar projects in the world have been funded, according to Department of Energy records. The administration’s approach has drawn vocal criticisms as well— Republicans accused the government of political favoritism and mismanaging public funds when the solar panel maker Solyndra went bankrupt last fall.

Dorothy Robyn, deputy undersecretary of defense for installations and environment, said that the renewable projects might be a game changer in the future as traditional power grids are increasingly vulnerable to aging infrastructure and attacks. She said the department is testing microgrid technology, which blends different forms of renewable energy so that grid load can be managed more efficiently.

“Together with advancing microgrid and storage technologies, renewable energy will allow military to maintain critical missions for weeks or months if the power grids go down,” she said.

The military has been pursuing alternative energy resources ranging from solar projects to biofuels for several years. DoD deployed a group of warships and fighter jets burning an expensive blend of recycled cooking grease, algae oil and petroleum in July.

However, the department’s search for unconventional energy sources, especially alternative fuels, has drawn criticisms from scholars and members of Congress. According to a 2011 report by the RAND corporation, a nonprofit global policy think tank, the military would derive no meaningful benefit from alternative fuels.

The report argues that most alternative fuel technologies are too expensive or too far away from commercial-scale use and urges the military to focus on energy efficiency instead.

But Will Rogers, a fellow with the Center for New American Security, a Washington-based think tank, said the quest for renewables ensures that the energy supply to core military missions is not susceptible to accidents and natural disasters.