JUNEAU — The U.S. Department of Energy has approved an order that would allow a proposed mega-gas project in Alaska to export liquefied natural gas overseas, though it remains unclear if the project decried by environmentalists will be built.

Thursday’s action reaffirms a 2020 authorization by the department that was challenged by environmentalists. The department undertook an additional review of the project, which led to the new decision.

Alaskans have long dreamed of a pipeline capable of carrying gas from the petroleum-rich North Slope to market. But a project has never come to fruition amid changes in the project’s direction under various governors, cost concerns and other factors.

The current project being pushed by the state-sponsored Alaska Gasline Development Corp. envisions a roughly 800-mile pipeline that would carry natural gas from the North Slope to Southcentral Alaska. The project would feature a liquefaction facility that would process, store and allow for the transport of liquefied natural gas.

Project backers have looked to Asia for potential partners.

Erin Colón, an attorney with the group Earthjustice, which has raised climate and environmental concerns with the project, said Friday the fact the gas line corporation has secured major approvals means the project “remains a threat,” even if it’s unclear when or if the project might be built.

“We have to defend against it regardless,” she said.

Frank Richards, president of the Alaska Gasline Development Corp., in a statement said an initial review of the decision indicates that it “adds to the record of support” for the project. He said the corporation will review the decision carefully as its work to further develop the project continues.