Wayne Sartore, vice president of northern pipeline development for Calgary-based Enbridge, said it makes sense for politicians to talk of simultaneous lines from the North Slope and Canada's Mackenzie Delta, but "we don't think it can be done.

"You just physically can't do it. There isn't enough equipment and workers available."

Enbridge, which operates the world's longest crude oil pipeline as well as an oil line from Norman Wells, Northwest Territories, has been taking a low-key approach in its race with Canada's other pipeline giants, TransCanada PipeLines and Westcoast Energy, to gain an edge in the Arctic project.

Enbridge chief executive officer Pat Daniel said his company is trying to help gas producers "evaluate which route is best, rather than proposing one over the other. We're afraid that will only create confusion in the regulatory process."

However, he said Enbridge intends "to be involved in either or both pipelines ... based on the fact that we operate in the north."

TCPL and Westcoast are joint partners in Foothills Pipe Lines, which has a two-decade approval to build the Alaska Highway line.

John Mawdsley, an analyst with FirstEnergy Capital, said the North American marketplace will eventually require gas from Alaska and the Mackenzie Delta.

But it's likely the Alaska project will proceed first because North Slope gas only needs a pipeline to start deliveries, while the delta is not close to production, he said.

"I think they will probably follow within one or two years of each other," Mawdsley said.