For the political and business leaders applauding a new vision for Union Station, now comes the hard part.

Amtrak enjoyed one compliment after another Wednesday at a news conference announcing a $7 billion proposal to expand and improve rail service at Union Station, in conjunction with a plan to build a 3 million-square-foot development behind the station.

D.C. Mayor Vincent C. Gray (D), who noted that he went to elementary school nearby, said the plan would create a “thriving, teeming, vital” transit hub for the city. Former mayor Anthony A. Williams (D), who lives a few blocks away on H Street NE, said the plan would make the station “a celebration of what is best about our city.”

And Del. Eleanor Holmes Norton (D-D.C.) said that the bold plan was the right first step, to demonstrate the station’s potential, and that the next step was determining how to pay for it.

“No plan for the decades fills in the funding details,” she said.

But now that the vision is public, stakeholders have begun to discuss the difficult task of turning the plan’s glossy images into reality.

John D. Porcari, the deputy U.S. transportation secretary and former Maryland transportation secretary, pledged support from the Obama administration.

A bigger, more modern Union Station is “an essential element of President Obama’s vision for high-speed rail in America,” Porcari said.

“To put it simply there is no do-nothing option,” he said. “It is either forwards or backwards. We’re looking at projections that Amtrak and commuter rail ridership at Union Station could more than double in the next 15 years alone.”

Williams, the newly named president of the Federal City Council, could play a key role in shepherding the project. As mayor, Williams had a leading role in some of of the District’s biggest infrastructure projects of the past 15 years, including the Walter E. Washington Convention Center and Nationals Park. The business group he now leads was instrumental in the creation of Metro and the construction of Verizon Center.

The post also affords Williams one of the five spots on the governing board of the Union Station Redevelopment Corp., the nonprofit organization that manages the historic rail hub and is searching for a new president to replace David S. Ball, who will leave at the end of the year.

Williams said he was confident that the private sector, Amtrak, and federal and local officials would support the vision.

“All of us are going to have to come together and work together on financing, come together, work together around the right organizational structure, come together, work together around the right program,” Williams said.

Amtrak officials have raised the prospect of partnerships with private-sector interests in real estate or transportation.

The transit agency could look to New York’s Penn Station for a model, according to Patrick L. Phillips, chief executive of the Urban Land Institute, a development research group. To develop Penn Station’s rail yards, New York issued financial and zoning incentives, extended a subway line and built the High Line public park.

“This is what’s happening around the world when you look at multi-modal transportation centers.

They create value, and that value can be shared among the public and the private,” Phillips said.

Other experts were skeptical.

“Any transportation project that’s going to attract a private investment has to have a fairly predictable revenue stream,” said an expert in private-public partnerships who asked not to be named because he had not studied the Union Station plan. “To come up with $7 billion is pretty challenging, for those kind of dollars, with that kind of asset. There haven’t been that many mega-billion-dollar public-private partnerships, and the bigger the project the more likely you’re going to have cost overruns.”

Union Station already has a real estate partner, District developer John E. “Chip” Akridge, whose company paid $10 million in 2006 for the right to build above the tracks behind Union Station.

Akridge plans a $1.5 billion development called Burnham Place. With as many as a dozen buildings and a reconnected street grid linking Capitol Hill, H Street and NoMa, Burnham Place would be bigger than City Center DC.

Burnham Place, he said, “will transform an ordinary overpass that exists today into a beautiful civic plaza, with a trolley stop and a grand entrance to Amtrak’s magnificent new train hall.”

There are economic benefits to that, Akridge added, and those are likely to outweigh even the $7 billion price tag.

“The economic benefits to this region are humongous,” Akridge said. “They are at least double the cost of putting this thing in.”