WASHINGTON – George Washington National Forest is more than just one of the largest expanses of pristine land in the East. It’s the leafy cradle for the Shenandoah, James and Potomac rivers, a source of drinking water for millions of people in greater Washington.

The forest — nearly 2 million acres of natural splendor straddling Virginia and West Virginia — might also hold another treasure: natural gas trapped under a deep layer of rock called the Marcellus Shale.

By the end of the month, the U.S. Forest Service is expected to decide whether to ban or allow the controversial method of drilling called hydraulic fracturing under the forest’s new, 15-year forest management plan. The decision will settle a raging dispute between conservationists and the oil and gas industry.

The industry argues it would be unfair for the government to “slam the door” on hydraulic fracturing in the forest for such a long period of time, and points out that natural gas is a cleaner fuel than coal.

Conservationists say the drilling method, also referred to as fracking, could contaminate water at its source. The process involves drilling a deep vertical well, then bending it horizontally so millions of gallons of water and toxic chemicals can be blasted into the earth to fracture shale and capture gas.

The Forest Service proposed banning the practice two years ago, a move criticized by Republican Gov. Robert McDonnell as overreach. But the proposed ban is backed by the U.S. Army Corps of Engineers, which operates the Washington Aqueduct, and the Fairfax County (Va.) Water Authority. Both agencies provide drinking water from the Potomac River to 4.5 million customers in the District of Columbia and Northern Virginia.

Thomas Jacobus, the Washington Aqueduct’s general manager, called the forest streams and rivers “a key resource,” and said in a letter to the Forest Service that anything that undermines agreements made by states to preserve the water quality of the Potomac “would be unwelcome. Safe water supply is essential to life.”

One hundred species of fish and mussels live in the shallow waters of the Cowpasture and Jackson rivers, which gurgle in the forest along the Appalachian spine. There are also 70 types of amphibians and reptiles, 180 species of birds and 60 species of mammals. The list of all the trees, plants, fishing areas, hiking trails and campsites could fill a book.

The forest streams and rivers, called headwaters, form in the region’s highest elevations and flow down. They are the origin of the Potomac’s drinking water and provide the water that created the James and Shenandoah rivers.

The officer in charge of drafting the final management plan said he understands the stakes of allowing drilling with chemicals in one of the most pristine forests on the East Coast.

“If you had a pollutant anywhere in the watershed, it would be a concern,” said Ken Landgraf, planning staff officer for George Washington National Forest. “But in the headwaters, everyone would have to deal with that. Everybody’s going to see that further downstream in the watershed.”

Another concern revolves around wastewater that bubbles back to the surfaces during the process and must be stored in sealed containers that have been known to leak. Dozens of heavy trucks carry the mixture of water and chemicals to and from the drilling sites, sometimes spilling it.

More than 500 million cubic feet of gas are entombed in Marcellus Shale, which runs 95,000 square miles between Virginia and Ohio. Fracking wells in Pennsylvania, West Virginia and Ohio have generated significant profits, as well as major concerns over safety.

The government has allowed oil and gas drilling on other public lands, mostly in the West. Production from about 92,000 of those oil and gas wells makes up about 13 percent of the nation’s natural-gas production and 5 percent of its oil production.

Landgraf said his team has pored over studies in New York, where hydraulic fracturing operations were numerous before a 2008 moratorium put them on hold. In addition, they have relied on records of safety incidents in Pennsylvania and West Virginia, along with U.S. Geological Survey records on fracking, to make their determination.

Under the current management plan, initiated in 1993 and originally set to expire in 2008, limited drilling was allowed. But, even though 12,000 acres are under lease by oil companies, the drilling never happened, in part because getting a permit was difficult.

Shale gas is “a potential domestic resource that at some point in time can be safely extracted,” said Mike Ward, executive director of the Virginia Petroleum Council, a nonprofit group that advocates for the oil industry. “We want flexibility to operate if improvements in the technology allow it. … To put a moratorium upfront slams the door without any further consideration.”