De’Angelo Wilson reaches the westernmost point near the Union Station parking garage as he conducts safety tests for the new D.C. streetcar line in Washington. (Katherine Frey/The Washington Post)

When Mayor Muriel E. Bowser (D) declared this week that the District’s era of broken streetcar promises was ending with her, the city’s new chief executive exuded a supreme confidence that she and her team can fix problems years in the making.

But meeting her pledge to expand and improve the city’s still-unopened streetcar line — which Bowser wants to see stretch nearly from Maryland’s border on the east to Georgetown on the west — will require wrestling vast challenges.

Among the unanswered questions: How would the expanded line be paid for? Who would build and operate it? Will the D.C. Council back the effort? Will there be enough riders to make the investment worthwhile? And are streetcars the best way to move people and spur economic development, two of the stated goals?

Even longtime streetcar backers acknowledge that Bowser and the rest of city government have a heavy lift.

“The numbers have to work. The organization has to be there. The planning has to be there. And the implementation has to be in the hands of people who are competent,” said council member Mary M. Cheh (D-Ward 3), chairwoman of the panel’s transportation committee. “It has to be something where people will regard it as a good ride, that it’s good transit. . . . It has to be really functional and practical, and people have to want to take it.”

Finding a way to achieve all that when the District has, over many years, not been able to do so will require effective decision-making across-the-board. One outstanding issue is whether the District can get around a federal prohibition against overhead streetcar power lines in much of the city. One option is buying streetcars that can run some distance without wires.

“We have to make decisions about overhead wires. We have to make decisions about fares. . . . We have to make a fundamental decision about any line from Union Station to Georgetown,” namely whether there is enough room to have dedicated streetcar lanes along K Street, Cheh said. Having a streetcar running alongside cars in regular traffic “is kind of an invitation to accidents and trouble with the efficiency of the line,” Cheh said, although she was describing only the situation along the city’s existing 2.2-mile line along H Street and Benning Road NE.

“If done right, that’s a big if . . . we’ll see the advantages of it,” Cheh said. “The economy depends on effective transportation. It’s very simple. We can’t have gridlock across the District.”

Bowser’s first city budget, due to be released Thursday, will reveal key details about her commitment and approach, and how she intends to make good on all of the promises she made Tuesday night in her first State of the District address.

The big immediate questions: Exactly how much does the mayor plan to dedicate to the streetcar system in the coming year? And how much is to be spent in later years as part of the city’s long-term capital spending plan?

Bowser on Tuesday called the streetcar program “long on promises and short on results.”

“That changes now,” she said.

“I promise you that we will get the streetcar along H Street and Benning Road up and running. Then we will extend the line to downtown Ward 7 so that council member [Yvette M.] Alexander’s constituents can get from Benning Road to H Street to Union Station and eventually all the way to Georgetown.”

Alexander (D-Ward 7) said she thinks there will be significant economic benefits to extending the streetcar line east along Benning Road and over the Anacostia River from the line’s current end point near Oklahoma Avenue NE. She is confident that Bowser will come through.

“I think its going to happen. I’m excited about it, because I think it can spur more development” all the way out to the Benning Road Metro station and beyond, Alexander said. She also is pleased with Bowser’s endorsement of an extension to Georgetown. Finding success with an expanded east-west line will drive support for additional lines, Alexander said.

“I think it’s been pretty much overall the consensus that we’ve invested this much, we have to at least see if this line is going to work, and we’re going to take it from there,” Alexander said. “I think this is just going to catapult future lines.”

Council member Jack Evans (D-Ward 2) said he is waiting to see dollar figures before making a public judgment.

“I have to see what the funding is for her vision,” Evans said.

He said the city is facing difficult choices about which long-term projects — schools, fire stations, bridges, roads, streetcars — it can build, given warnings from bond-rating agencies about the city’s heavy debt burden. “You have to make choices. You cannot do everything,” he said.

Council Chairman Phil Mendelson (D) led an effort last year to sharply curtail future spending outlined for the streetcar, leading to a dramatic pullback in the city’s far-reaching plans to build a 22-mile, and eventually a 37-mile, system. But last year’s six-year streetcar-related budget reached $587 million, including money for replacing the Hopscotch Bridge behind Union Station, Mendelson noted.

“Mayor [Vincent C.] Gray said we had essentially killed the program by leaving it with over a half-billion dollars, which did not make any sense to me,” Mendelson said.

Mendelson said he supports extending the line to the Benning Road Metro, and making initial investments over the next year or two on planning the K Street extension to Georgetown. But he said he wants to see how the H Street and Benning Road line works in practice “before we spend significant bucks on extending the system further.”