Alpha Natural Resources, once a powerhouse of the American coal industry, filed for Chapter 11 bankruptcy protection on Monday so it may emerge from the grip of a $3 billion debt at a time when utilities are switching to natural gas and coal prices are plummeting.

Alpha Natural Resources borrowed heavily in 2011 to buy Massey Energy for $7.1 billion, seeking, like many coal companies at the time, to acquire an empire of Appalachian coal mines in the hope that China would be a growth market for exports. That deal turned out to be a disaster for the company when demand for both steel-making and power-generating coal declined domestically and in several important international markets in recent years.

“The change and challenges the U.S. coal industry has experienced over the last several years are greater than any in the past three decades,” Kevin S. Crutchfield, Alpha’s chairman and chief executive, said in a statement released by the company. “There is no doubt more uncertainty ahead, but also transformational opportunity in the coal sector for those who make proactive, strategic decisions.”

The coal industry suffers from multiple problems. Natural gas prices have swooned in recent years, leading many utilities to switch from coal. The Obama administration on Monday unveiled a set of Environmental Protection Agency regulations that could close hundreds more coal-fired generation plants.

At the same time, China, which consumes 45 percent of the world’s coal, is steeply reducing the burning of coal to combat urban air pollution. And the strength of the dollar is reducing the competitiveness of U.S. coal producers.

The result has been plunging coal production in the United States, down by 15 percent since 2008. Still, stockpiles are mounting at mines as coal-fired power plants shut down month after month.

The Energy Department expects a further drop of 70 million tons in coal production this year mainly because of a 7 percent decrease in demand by the electric power sector, which, in addition to natural gas, is increasingly turning to renewable energy sources like wind and solar power.

Only a decade ago, coal supplied roughly half of the source of power for the country’s utilities; that percentage has dropped to about 40 percent. The Energy Department projects that coal will continue to lose market share over the next decade, although it will continue to be an importance source of energy.

“We are going to continue to see bankruptcies so the industry can get down to a size in terms of total capacity and output to have the financial wherewithal to be attractive assets at depressed prices and then operate profitably,” said John Lichtenstein, an Accenture Strategy managing director who advises coal producers.

Alpha, which is based in Bristol, Virginia, suffered four straight years of losses in large part because most of its business is in Appalachia, where mining operations tend to be more expensive than other parts of the country. For the last three years it has been forced to close much of its fleet of mines to reduce costs, shaving its payroll by roughly 4,000 workers, or more than a quarter of its workforce.

To make matters worse, Wyoming regulators recently told the company it no longer qualified for a program that allowed the company not to buy insurance to cover future mine cleanup costs.

Alpha, which still operates 50 mines in several states, said it secured a financing package of $692 million arranged by Citigroup.

It is at least the seventh coal company to go into bankruptcy over the last year. Most of the other coal companies have been small, although another major company, Walter Energy, filed for bankruptcy protection last month with a plan to give control of the company to senior creditors.

Such a turn of events was hard to envision even five years ago, as Alpha and other coal companies went on a buying spree. Coal prices were high, global demand was galloping along with the surging Chinese economy, and their earnings were peaking.

Alpha acquired Foundation Coal to extend its operations to the western Powder River Basin, where coal can be cheaply mined off the surface and the promise of exports to Asia was high. And then it made the Massey Energy purchase in 2011 after that company went into a tailspin following the Upper Big Branch mine disaster in which 29 miners died in an explosion. The acquisition was based on an assumption that developing countries had an insatiable appetite for Appalachia’s high-heat-producing coal for steel making.

Wall Street analysts said the reorganization of the industry was inevitable and that the losers would be the equity holders and the banks, and owners of the debt acquired at face value. But much of that debt has already changed hands at pennies to the dollar, and the new holders of the debt will most likely acquire most of the new equity in the companies after they are reorganized.

The other possible savior for the coal industry, according to some analysts, is China, although that could take some policy changes in Beijing.

“We could see foreign capital coming into the industry within two years,” Lichtenstein said, “when things hit bottom and if the dollar weakens.”