Construction of a four-lane bridge across the St. Croix River to Wisconsin would ruin a federally protected wild and scenic river and create a "terrible precedent" for similar cases around the country, an attorney for the Sierra Club argued Monday in federal court in Minneapolis.

"In spite of its protected status the Lower St. Croix is in jeopardy again," said Michael Soules, who asked Chief Judge Michael Davis to stop four federal agencies from authorizing or financing the proposed St. Croix River Crossing bridge.

In response, three government attorneys attempted to discredit a Sierra Club suit opposing the bridge as sour grapes, saying the club didn't like the agreement that resulted from years of negotiations among various stakeholders.

"This was a compromise reached among competing concerns," said U.S. Attorney Fred Siekert.

The hearing was the latest step in a decades-long battle in government meeting rooms and in court to decide whether the laws and policies that govern the St. Croix will permit a new bridge, which would be the costliest in Minnesota history.

The showdown has been years in the making and stakes are high: To environmentalists, the bridge would promote urban sprawl, ruin the river's scenery and damage its fragile ecosystem. To proponents, the bridge would alleviate traffic congestion, compensate for substantial growth that's already underway and improve the river's recreational value by removing dilapidated structures and creating a loop bicycle and pedestrian trail.

The cost of the bridge, if construction were to begin in 2013, is estimated at $668.5 million. The bridge would link Washington County with a growing suburban region in St. Croix County and launch from Hwy. 36 at Oak Park Heights. The proposed bridge's cost is six times the estimate of just a decade ago and more than twice what another new bridge over the Mississippi River at Hastings will cost.

Soules directed much of his criticism at the National Park Service (NPS) for "arbitrary reversal" of its 1996 position that the bridge would harm the St. Croix. The Sierra Club successfully won a suit in 1998 to stop the earlier proposal.

"It remains undisputed that the current proposed bridge is even more massive than its predecessor," Soules told the judge.

But Siekert said that current NPS support resulted from a "mitigation package" that included fewer piers, a different design and bluff-line improvements. "This project cleans up the Lower St. Croix in a way that's never been done before," he said.

Also at issue at the Monday court hearing was the 1931 Stillwater lift bridge, which would close to vehicle traffic and become part of a loop trail that would circle into Wisconsin if a new bridge is built. Attorneys argued over the meaning of a "no net increase" -- stipulated in a 2001 management plan -- in the number of bridges crossing the St. Croix.

In his arguments, Soules outlined several points where he contended the agencies have violated laws or policies that protect the St. Croix. But attorney Richard Moriarty, representing the Wisconsin Department of Justice, refuted those legal points in detail and said the Sierra Club suit ignores decisions and agreements that resulted from decades of negotiations.

"Ultimately the Sierra Club is merely unsatisfied with the results," he argued.

Davis said he would take the matter under advisement. No date was set for a decision.

Kevin Giles • 612-673-4432