WASHINGTON - President Obama signed legislation Wednesday authorizing construction of the long-awaited St. Croix River bridge, ending decades of debate, planning and litigation with the stroke of a pen.

The president's signature comes two weeks after Congress gave the needed environmental clearances for the $690 million project, the largest public works project in state history.

"Basically, the bill is done, and the bridge will be built," said U.S. Sen. Amy Klobuchar, the Minnesota Democrat who authored the final legislation granting the project an exemption from the Wild and Scenic Rivers Act, a landmark environmental law authored by her political mentor, former Vice President Walter Mondale.

Bridge backers in Minnesota expressed relief. The proposed span connecting Minnesota and Wisconsin has roiled the community for years, pitting residents trying to ease congestion in the historic city of Stillwater against environmentalists seeking to protect the waterway.

"We're going to get our city back," said Doug Menikheim, a Stillwater City Council member who has said that heavy commuter traffic was turning city streets into a state highway.

Critics were crushed, saying the first-ever exemption from the river protection act will make it easier for other communities to move ahead with development that jeopardizes cherished waterways.

"We are extremely disappointed that Congress chose to move in this direction," said Christine Goepfert of the St. Paul office of the National Parks Conservation Association. "It sends a message that if you want to build a project, this is a way to do it."

Right down to the end, despite overwhelming votes in both the House and Senate, the bridge divided Democrats inside and outside the administration. While pro-labor Democrats emphasized the jobs potential of the project, Mondale and officials inside the Interior Department raised flags about granting such a conspicuous exemption to a law intended to protect scenic rivers.

A rare bipartisan alliance

After the final vote in the House, Klobuchar and Minnesota Republican Rep. Michele Bachmann joined in writing a letter to Obama seeking his "prompt signature" on the bill, which had languished in Congress for months.

Bachmann went a step further, calling on the president to hold a public signing ceremony for the bill, which she shepherded through the House as part of an unusual alliance with Klobuchar and other top state DFLers, including Gov. Mark Dayton, who demanded a March 15 deadline for congressional action.

But in the end, the president's signature was neither prompt nor public. The White House made Obama's signature public in a statement from regional spokeswoman Caroline Hughes, who called the bridge "a project that will promote travel and commerce between the states of Minnesota and Wisconsin for years to come."

Hughes' statement praised Klobuchar's "efforts to pass this bipartisan legislation," but did not mention Bachmann, who spent much of the last year on the presidential campaign trail taking daily shots at Obama and his record on the economy.

Against a partisan backdrop that is likely to remain divisive, Bachmann did receive credit from Sen. Al Franken, a Democrat who argued for the jobs and economic benefits of the bridge. Franken said the project will "create thousands of jobs and deal with the serious traffic problems that were hurting business and tourism in the Stillwater area."

Despite their political differences, Klobuchar and Bachmann could reap election-year rewards for breaking the impasse on the hard-fought bridge proposal, a legacy-building project for the state.

"It finally took congressional action to allow this project to proceed because of years of frivolous lawsuits and bureaucratic holdups," Bachmann said. "But I'm pleased we could deliver."

Signing lag was routine

Despite environmental and fiscal objections raised in Congress by Minnesota Reps. Betty McCollum and Keith Ellison, Klobuchar and Bachmann said that there was never any doubt that Obama would sign the bill.

Klobuchar called the two-week time lag, just three days short of a legal deadline, a matter of routine. "It wasn't at all because of any issues with the bill," she said.

Although Interior Secretary Ken Salazar and his staff had raised concerns about the project in congressional testimony, Klobuchar said she had been consulting with Transportation Secretary Ray LaHood, a former Republican congressman from Illinois who had offered to mediate the bridge dispute.

Congressional opponents apparently did not lobby the White House to block the bill. And although debate is likely to continue unabated in Minnesota, Klobuchar said, "We've reached the point where it's time for the bridge to be built."

Jon Chiglo, the project's new leader at the Minnesota Department of Transportation, will begin pressing ahead.

"We're focused on moving on this job forward and building this crossing," he said.

'An incredible journey'

Transportation Department officials will begin testing the river bottom to find the ideal location for piers, buy more land and tackle the costly problem of utility relocation work in Oak Park Heights, where a major approach to the new bridge will be built.

"It's a time for celebration," said Washington County Commissioner Gary Kriesel, who represents the district that includes Stillwater and Oak Park Heights. "It's probably the oldest, longest-living project in the history of MnDOT. It's been an incredible journey over the last 20 to 30 years."

Dennis Hegberg, the board chairman, took dead aim at critics who have questioned the need for a massive bridge to a sparsely populated outpost in western Wisconsin. "It's not a bridge to nowhere," he said.

Kevin Diaz is a correspondent in the Star Tribune Washington Bureau.