But Mr. de Blasio, who has been criticized as being slow to follow up on his own proposal, said Wednesday that it was “time for our transit system to catch up” with the explosive growth along the waterfront.

“The BQX is one of the biggest, most ambitious projects in a generation,” the mayor said in a statement. “It will be a challenge, but New York City is taking it on.”

The streetcar system, which would run on rails and be powered by overhead wires, was initially expected to pay for its own construction through extra tax revenue brought in by the increase in property values it would trigger along its route.

But a $1.3 billion funding gap has opened up, mostly because of a 2016 city policy that earmarks much of the increase in tax revenue for other purposes, including affordable housing, making it unavailable for the streetcar, Deputy Mayor Alicia Glen said.

It is that gap that the city is looking to Washington to help close. Ms. Glen said that the public-private partnership that would build the streetcar would be expected to contribute up to 10 percent of the cost, leaving about $1 billion to come from the federal government.

Though President Trump has slashed funding on many fronts, including withdrawing support for the $30 billion Gateway commuter rail project connecting New York and New Jersey, city officials noted that Congress has restored money for Gateway through the appropriations process.

The streetcar — which would link Red Hook, Williamsburg, Greenpoint, Long Island City and other places that have seen crumbling industrial waterfronts replaced by new housing and jobs — was met with both enthusiasm and skepticism when Mr. de Blasio proposed it. Critics asked why buses along the same route could not be used instead.