Dan Janison Melville. N.Y. Tuesday January 26, 2010. Daniel Janison,

Dan Janison has been a columnist at Newsday since 2007.

Anyone daring to lay odds on the viability of Mayor Bill de Blasio’s big proposal for an electric street-car line linking waterfront neighborhoods in Queens and Brooklyn should consider a cluster of tricky challenges waiting around the corner.

“Not easy,” said a skeptic in a casual conversation before the mayor’s latest press conference in a Red Hook exhibition hall.

“Worth it,” replied a de Blasio official.

As he did in his state-of-the-city speech Feb. 4, de Blasio — surrounded by top aides, community representatives and elected officials — evoked New York City’s transformations.

A true five-borough economy needs new transit to reach new job hubs, he said.

Easing inequality means relieving the isolation of lower-income areas, he said.

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Helping the environment requires improving mass transit, de Blasio said.

“The entire transit system of this city was built for decades and decades and decades with a single goal — get people from the outer boroughs into Manhattan and vice-versa,” he said.

So this state-of-the-art, zero-emissions light-rail line, currently priced at $2.5 billion, would use 60 cars over its 16-mile route between Astoria and Sunset Park, and boost tax revenues by improved economic activity, officials said. It would land, maybe every half-mile, at various subway, bus and ferry stops.

But many details remain to be filled in if de Blasio is to get his way and see the project “shovel-ready” by 2019.

Underground pipes and mains must be dug up and moved.

Furthermore, a still-uncounted number of parking spaces would need to be permanently eliminated on major streets to accommodate the new mass-transit link. That doesn’t sound like a popular selling point.

“We don’t yet have a sense of what the impact would be on parking, because the routes still have to be refined,” de Blasio said 43 minutes into his press conference. “We’re going to be sensitive to that . . . but given the many benefits [of the project] it will be more than appropriate in terms of a tradeoff.”

The city would build this so-called BQX street-car line independent of Gov. Andrew M. Cuomo’s Metropolitan Transportation Authority. That might sidestep the current alienation between the mayor and governor. But it also leaves unknown whether fares, to be set at the same level as the MTA’s, could be paid by Metrocard and how transfers might work.

The belief in affected areas as to whether this line will really help thousands of Housing Authority residents, or promote gentrification, has yet to be gauged.

Rep. Nydia Velasquez hailed the mayor, but warned: “The affected communities must be consulted. We must ensure working families fully benefit and that it is affordable.” De Blasio pledged “a very intensive engagement process.”

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Tucker Reed, president of the Downtown Brooklyn Partnership, told de Blasio: “There will be a lot of naysayers in the next couple of weeks that’ll say why this can’t be done.

But, Reed added, “There will be millions of New Yorkers who will thank you in generations to come.”

Wherever it goes, the push has begun.