WASHINGTON — The Environmental Protection Agency will start the first federal probe into whether the controversial drilling technique known as hydraulic fracturing is spoiling and diminishing drinking water supplies.

The agency’s final study plan was released today.

The research will look at where companies performing hydraulic fracturing get their water and how much they use. It will also try to pinpoint the cause of alleged water contamination — looking at aboveground spills, well design and the fracturing process itself.

The first results will be available in 2012.

Meanwhile, the agency has taken steps to boost regulation of so-called fracking, which is the injection of water and chemicals underground to extract natural gas trapped in rock.

The EPA will examine drilling sites in Pennsylvania, North Dakota, Louisiana, Texas and Colorado.