WASHINGTON - After decades of legal wrangling and legislative maneuvering, the battle over the St. Croix River crossing is coming down to its final hours.

The U.S. House is now scheduled to vote Thursday on the fate of the proposed $690 million project, a four-lane span that requires a congressional exemption from the Wild and Scenic Rivers Act, a landmark environmental law authored in 1968 by former U.S. Senator and Vice President Walter Mondale.

The bridge won unanimous support in the Senate, where it was shepherded through last month by Minnesota Democrat Amy Klobuchar. But the project has encountered turbulence in the House, where chief author Michele Bachmann, a former GOP presidential candidate, found her efforts stymied in a legislative quagmire.

"It really is like Moses parting the waters to be able to get this done," Bachmann said Tuesday amid a flurry of last-ditch lobbying. "We are working the phones, pounding the pavement and knocking on doors."

Opposing Bachmann, as well as Gov. Mark Dayton and other top Minnesota DFLers, is U.S. Rep. Betty McCollum, who urged House colleagues Tuesday to vote down the proposed "mega-bridge" between Oak Park Heights and Houlton, Wis. McCollum acknowledged the existing Stillwater Lift Bridge is antiquated and needs replacing, but has called for a cheaper, scaled-down version. The proposal before the House, she said, "is not just a bridge, but a monument to government waste."

Upping the ante in the long-standing debate is a fast-track process called a "suspension calendar" that requires approval by two-thirds of the House to prevail. It is normally reserved for naming post offices and other non-controversial measures.

Bachmann said she originally sought to include the bridge project in a major highway bill making its way through the Transportation Committee. But that bill has bogged down in recent weeks, and might have run afoul of a March 15 deadline Dayton has set for either getting a go-ahead from Congress or reallocating the money for other infrastructure needs.

The rarity of using an expedited procedure for a hotly contested project like the St. Croix bridge underscores the stakes after months of legislative impasse. "We were able," Bachmann said, "because of the urgency of the hour to get the [GOP] leadership to be willing to take the bill up."

Democrats divided

Support for the bridge has been bipartisan, but it has run into opposition from some Democrats and fiscal conservatives who deride it as a "bridge to nowhere."

An anti-pork group called Taxpayers for Common Sense wrote to Transportation Committee members this week saying the bridge is "too large in scope and therefore far too expensive for taxpayers."

Mondale, who lives about 20 miles from the proposed bridge site, also has joined the fray. In a letter to House Democrats earlier this month, he called the project an "assault upon our beautiful river and a precedent for further predations directed against all our federally protected rivers."

Dayton, who backs the current bridge plan, fired off letters Tuesday to House Speaker John Boehner and Democratic Leader Nancy Pelosi. While McCollum and fellow Minnesota Democrat Keith Ellison have called for redesigning a smaller bridge, Dayton said further delay "would likely be its death knell."

Opposition to the span has been intense but fragmented. Meanwhile, bridge proponents have been able to unify Republicans and Democrats under the banner of economic development and job creation.

"It's one of those projects where there have been hurdles for 30 years," said Klobuchar, who became Bachmann's unlikely ally in the bridge fight. "There is no way you're going to get it done with just one party."

The bridge issue also has split Washington County residents. Proponents say a larger, safer bridge will push traffic congestion out of Stillwater. Opponents say it's too big, too costly and could just shift Stillwater's traffic problems to neighboring Oak Park Heights.

Bachmann will need bipartisan support to pass the bill. Even if she rallied the entire 242-member GOP caucus, she would still need at least 48 Democrats to reach the 290-vote threshold needed for two-thirds passage.

Plan B

But Bachmann also has a potential insurance policy. If she loses on the vote this week, her office has been told by GOP leaders that the bridge bill could get a second vote next week under regular procedures that require only a simple majority.

Activists on both sides say passage is likely on Thursday, though not assured. Helping Bachmann's case is the reluctance of House members to interfere in each other's districts, whatever their reservations.

Accordingly, bridge backers are emphasizing local control as they make their final pitches. Brandon Moody, chief of staff to Wisconsin Republican Rep. Sean Duffy, said Duffy has talked up the need for "setting a precedent, that regulatory hurdles should not get in the way of the states' rights to proceed with building infrastructure they feel is important."

McCollum countered in a letter Tuesday that "creating a congressional exemption in federal law is not a local issue -- especially when hundreds of millions of taxpayer dollars are on the line."

Staff writer Kevin Giles contributed to this report. Kevin Diaz is a correspondent in the Star Tribune Washington Bureau.