The Silver Spring Transit Center, which is years behind schedule and over budget, is seen in this file photo. (Sarah L. Voisin/The Washington Post)

Repairs to the Silver Spring Transit Center will require another $21 million, Montgomery County officials said Thursday, bringing the cost of the beleaguered project — now four years behind schedule — to $141 million, more than $50 million over original estimates.

County officials said in September that additional funds would be needed to fix construction and design defects in the three-level commuter terminal adjacent to the Silver Spring Metro station at Colesville Road and Georgia Avenue. But until Thursday, they did not say how much. The deficiencies in the facility include poor-quality concrete and lack of steel supports for roadways that are expected to support hundreds of buses arriving and leaving each day.

General Services Director David Dise, the lead county official on the project, said the $21 million should be enough to complete the repairs by late April or early May. “This is all the work that needs to be done,” he said.

There is no firm opening date. After repairs are finished, the Washington Metropolitan Area Transit Authority, which will operate the center as part of its transit system, has up to 60 days to inspect the facility and decide whether it is ready for passengers.

To complete the project, the county has decided to front the money for the repairs and then try to recover it by suing the contractors that it holds responsible for the problems — a process that could take years.

In a letter to County Council President George Leventhal (D-At Large), County Executive Isiah Leggett (D) again pledged taxpayers will not be on the hook for the additional expense.

“The contractors and consultants responsible will be held fully accountable for all costs related to and resulting from the necessary remediation,” Leggett said.

Foulger-Pratt is the lead construction contractor. The structure was designed by Parsons Brinckerhoff.

The proposal requires council action to approve using $16.7 million in revenue from general obligation bonds. A resolution will be introduced at Tuesday’s council meeting. A public hearing will be scheduled, with final council action expected Jan. 13.

The balance of the $21.2 million, Leggett said, will come from surpluses remaining on finished projects and from shifting funds away from three other projects that are underway but not complete.

Officials emphasized that the transfer of funds away from the North Potomac Community Recreation Center in Rockville, the Glenmont fire station and the Ross Boddy Neighborhood Recreation Center in Sandy Spring will not delay the opening of those facilities.

They said each is behind schedule for various reasons and the money being shifted would not have been spent in the current fiscal year. Officials said they can restore the money for each ofthose projects in future capital budgets.

Dise said the remaining work at the transit center includes construction of additional supporting concrete beams and steel supports. When the weather warms in the early spring, another layer of latex-modified concrete will be added to one of the levels.

Council members said Thursday that the added expense is not welcome, but that they think they have little choice but to approve Leggett’s request.

“We’ll probably hold our noses and vote for it,” said Leventhal, “and work hard to make sure taxpayers are reimbursed. It’s a bitter pill to swallow.”

Council member Roger Berliner (D-Potomac-Bethesda), chair of the council’s Transportation and Environment Committee, said “there’s no option” but to authorize the spending.

“We need to finish this work,” Berliner said. “We need to deliver this to the public as soon as possible.