Environmental groups and the Obama administration have long promoted natural gas as a domestic energy source that is cleaner and cheaper than oil and offers a way for the United States to break its dependence on foreign energy suppliers. But a drilling method being used to unlock gas deposits deep inside the Earth has led to widespread protests. Hydraulic fracturing, or “fracking,” involves injecting massive amounts of water, chemicals, sand and other material under high pressure into shale formations to break the rock and release the gas trapped inside. Critics say fracking fouls drinking water, pollutes the atmosphere with toxic methane gas and turns rural communities into ugly industrial zones. Energy executives say, however, that the technique is safe and efficient and is creating thousands of jobs. In Congress, lawmakers have introduced bills to tighten environmental regulation of fracking, and some states have banned the procedure while they study its impact.