The state Department of Environmental Quality and the United States Forest Service approved the operating plan for the Sterling Mining Company's Rock Creek Mine on Wednesday. The company wants to extract 10,000 tons of copper and silver ore a day for 30 to 35 years from the wilderness area.

The project will take at least five years of development before construction begins.

The Rock Creek project, which is believed to contain the fifth richest deposit of silver in the United States, would be just above the Clark Fork River on the edge of the Cabinet Mountains Wilderness. The mine would tunnel 900 feet beneath the wilderness area.

The pine-draped Cabinet Mountains are an important habitat for the protected bull trout and for an isolated population of about 20 grizzly bears. Environmentalists have opposed the project for years, fearing that the species will be harmed. They say they will appeal the decision.

"The grizzly population is in trouble as it is," said Bob Decker, executive director of the Montana Wilderness Association in Helena. "And the mine will be a major intrusion into their habitat."

But Frank D. Duval, president of Sterling Mining in Spokane, Wash., said experts had determined that the mine could operate without environmental harm.

"It's been studied for 14 years by numerous consultants, biologists, hydrologists, geologists, scientists," Mr. Duval said. "They have done a huge amount of study."

The permit comes at a time when the mining industry in Montana is fading, largely because of low metal prices. This year, the Montana Mining Association, a trade group, closed when it ran out of financing.

Mr. Duval said current metal prices did not matter.

"You really don't know what the price is going to be when you are ready to run it," Mr. Duval said. "You go ahead knowing it will take a lot of time with delays and hope prices are good."

The Forest Service says that even though the project is on the edge of the Cabinet Mountains Wilderness and partly in the Kootenai National Forest, it is allowable under the Mining Law of 1872, which permits companies to stake claims to publicly owned minerals for small processing fees.

"We have to give them access to those mineral rights by law," said John McKay, a Forest Service geologist who oversaw the 2,750-page environmental impact study. "We can only mitigate the damage."

Mr. McKay said the project was an underground mine, not an open pit. It will have two openings, which will look like highway tunnels, and a processing facility "about the size of a Wal-Mart." He said the tailings, or waste from the mine, would be a paste, not a liquid, in an effort to minimize the potential for water pollution in the Clark Fork.