The 25 assumptions, covering such topics as wind speed and direction, oil-spill duration and recovery rates, were adopted illegally when DEC met with industry officials behind closed doors in 1997, said Jenna App, the attorney for the plaintiffs.

"Some of them are unrealistic," said App, adding that internal department reviews have raised questions about at least 15. "DEC knows that these are flawed. So there's a problem with DEC failing to act."

The lawsuit also charges DEC with violating state law by not subjecting oil-spill contingency plans to a review under the Alaska Coastal Management Program.

The lawsuit asks the court to declare the state to be in violation of its own environmental laws, and for an order barring use of the 25 assumptions for oil-spill planning.

The plaintiffs are the Alaska Forum for Environmental Responsibility, the Northern Alaska Environmental Center, Cook Inlet Keeper and the Sierra Club.

A DEC manager defended the department's use of assumptions, saying they help guide its oil-spill planning but are not themselves significant.

"This is a planning exercise. None of these are performance standards," said Larry Dietrick, DEC's director of spill prevention and response. "A spill contingency plan is a theoretical response to a theoretical oil spill using theoretical assumptions."

The lawsuit is the latest in a series of charges leveled at DEC, which critics say has a history of buckling under pressure from the oil industry, a potent force in Alaska's economy.