MONTPELIER, Vt. — Environmental regulators ruled Monday that Vermont’s Act 250 land use law would apply to any proposal to reverse the flow in an oil pipeline system that crosses northern Vermont.

The ruling from the District 7 Environmental Commission coordinator in St. Johnsbury is a victory for environmentalists amid fierce debate over another pipeline, the proposed Keystone XL pipeline to move tar sands oil from Alberta to Texas.

Groups like the National Wildlife Federation and the Vermont Natural Resources Council have expressed concern that the pipeline that now carries oil from South Portland, Maine, to Montreal, could have its flow reversed and carry Canadian tar sands oil through Vermont, New Hampshire and western Maine.

The Portland-Montreal Pipe Line Corp. has 30 days to ask for reconsideration and could then appeal to the state Environmental Court and the state Supreme Court.

Spokesman Tim O’Meara said the company was reviewing the decision and would have no immediate comment.

The ruling by Kirsten Sultan, coordinator of the District 7 Environmental Commission, said reversing the flow in the pipeline — really three pipelines running in parallel for about 60 miles through northeastern Vermont — would be a “substantial change” in use of the infrastructure and would warrant review under Act 250.

Under that 1970 law, development projects affecting more than 10 acres are subject to review first by a regional District Environmental Commission; decisions can be appealed to the state Environmental Court and the Vermont Supreme Court. Decisions turn on 10 criteria, ranging from impacts on traffic to aesthetics.

Monday’s decision cited a July 2010 spill of more than 1 million gallons of tar sands oil from a pipeline near the Kalamazoo River in Michigan. “The tar sands oil sank to the river bottom, coating wildlife, rocks, and sediment. Cleanup from this spill is incomplete, with costs at $800 million and rising,” Sultan wrote.

Sultan wrote that several Act 250 criteria apply because of the “potential impact from an unplanned spill event.”

Vermont environmental groups and some northeastern Vermont land owners are hailing the ruling.

Johanna Miller of the Vermont Natural Resources Council is calling the decision great news. She and Sandra Levine of the Conservation Law Foundation say it will give Vermonters a voice in whether tar sands oil should be shipped across the state.