There's an old saying -- "where the rubber meets the road" -- to characterize situations in which policy meets up with real life. On Thursday, it was an especially apt description of what happened in a colorless St. Paul meeting room when the Minnesota Public Utilities Commission took up the fate of the proposed Big Stone II coal-fired power plant.

To be built just across the border in South Dakota, Big Stone II has sparked one of the biggest regional environmental controversies in recent years. Environmentalists oppose the plant largely because they fear its carbon dioxide emissions will contribute to global warming. On the other side are five utility companies, led by Otter Tail Power Co., that believe the new plant is critical to meet electricity demand.

South Dakota has already greenlighted construction of the $1.6 billion plant. But its fate may well rest in the hands of Minnesota's five relatively unknown utilities commissioners, who are weighing whether to approve new power lines to carry the plant-generated energy into Minnesota. If the commissioners vote no, plant backers may scuttle the project.

The decision is one of the most bitterly contested in the history of the commission. It's also a harbinger of increasingly difficult decisions as the nation transitions from fossil fuels to renewable energy technology that's still being refined. More than ever, commissioners will need to strike a balance between meeting the region's need for reliable energy, keeping rates affordable, and pushing to meet the aggressive environmental goals called for by Gov. Tim Pawlenty and the Legislature.

There's no clearer example of that than Big Stone II. A decade ago, the proposed lines likely would have sailed through. But in 2007, the Minnesota Legislature approved one of the nation's most farsighted climate change action plans, calling for substantial reductions in state greenhouse emissions.

The commission rightly saw the Big Stone II project as not merely being about new power lines, but also about commitment to Minnesota's new goals. State law requires the utilities to prove the transmission lines are needed and that less expensive conservation measures and alternative energy such as wind power would not suffice.

But on Thursday, commissioners also were asking two broader but equally important questions: Given the new climate change goals, does the state want to take a contradictory stance on a carbon-emitting coal plant? Or, from a different perspective, is the plant a bridge to a future when alternative energy is widespread and its technology perfected?

In a hearing room filled with more than 100 utility executives and environmental advocates, there were sighs of exasperation Thursday when commissioners decided to postpone their decision to gather more information. But the fight over this plant has raged for four years. If commissioners -- particularly if Dennis O'Brien, a new member of the board -- need a few more months, so be it. Much is at stake. Commissioners must be absolutely certain they get it right.