The Washington Monument will remain closed until additional repairs are made to its troubled elevator. (Carolyn Kaster/AP)

Billionaire philanthropist David Rubenstein has agreed to fund an overhaul of the Washington Monument’s broken elevator system, but the beleaguered landmark will probably remain closed for the next 2 1/2  years, the National Park Service says.

It is the second time that Rubenstein has come to the aid of the monument, which has been shuttered since Aug. 17 because of chronic elevator problems.

After the 2011 earthquake, he donated $7.5 million of the $15 million cost of repairing the marble-and-granite obelisk.

But there is no start date for the roughly 12-month elevator project, which will cost $2 million to $3 million, because the Park Service is awaiting funds for a new security screening entrance that it wants to build at the same time.

And even if those funds come through, the Park Service does not see the monument reopening until the “cherry blossom season in 2019,” a spokesman, Mike Litterst, said in an email.

“It does seem like it’s a long period of time,” said Will Shafroth, president of the National Park Foundation, the charitable partner that is facilitating Rubenstein’s donation. “Just know that the Park Service is moving as fast as it can.”

“As frustrating as it can be, they’re a federal agency,” he said. “We’re talking about one of our national monuments . . . A lot of people have a say in it, and it tends to grind the process a little bit slower than we’d like.”

The centerpiece of the Mall, the monument had just reopened two years ago after an almost three-year shutdown after the earthquake.

Normally entered by about 500,000 visitors a year, the 555-foot icon is a hallowed symbol of the United States and of Washington.

“It’s the first thing people see when they come to the city,” said Sean Kennealy, chief of the professional services division for the Park Service’s National Mall and Memorial Parks.

Construction began in 1848. It was dedicated in 1885 and honors George Washington, a Revolutionary War hero and the nation’s first president.

The Park Service says the elevator, which carries visitors to an observation level where the views are spectacular, is too unreliable to resume operations.

It broke down numerous times in recent months, stranding groups of visitors and staff on board or at upper levels, and requiring calls to the D.C. fire department.

Rubenstein is a founder of the Carlyle Group, a Washington-based global private equity firm, and has been a major benefactor of historic sites and institutions across the region.

This year, he announced an $18.5 million donation to help renovate the Lincoln Memorial.

Last year, he pledged a $5.37 million donation to refurbish the U.S. Marine Corps War Memorial near Arlington National Cemetery.

In 2014, he gave $10 million to Montpelier, the historic Orange, Va., home of James Madison; $5 million to the White House Visitor Center; and $12.3 million to Arlington House, the home of Robert E. Lee. He said his goal after the earthquake was to get the monument reopened to the public as soon as possible, and the goal is the same now.

“The thing to do is to make the place as hospitable as possible and as safe as possible,” he said. “It’s a monument that’s going to be around for another 100, 200, 300 years, who knows how long.”

“Obviously, like everybody, I wish it was ready tomorrow,” he said. “But that’s not realistic. I want to make sure it’s done right, and if that’s what they say it takes, that’s what it takes.”

As for the elevator, “It was a very difficult decision to say that we need to close . . . until we can completely modernize this,” said Gay E. Vietzke, superintendent of the National Mall and Memorial Parks.

“But we really felt that we owed the public a positive, seamless experience,” she said. “And we were at a place where we couldn’t offer that.” She called it “ an unpredictable situation.”

“Say you’re [stuck] in the cab . . . and you have 30 or 40 minutes to wait” for emergency crews, Vietzke said. “And you’re claustrophobic, or someone’s sick, or has a condition.”

The elevator problems came just as the Park Service was about to launch an 18-month, $9 million project to build the permanent security screening facility. The present facility is temporary.

That project, which also would require closing the monument, is awaiting government funding, Vietzke said. The Park Service wants to proceed with the two projects simultaneously, so it can save money and avoid one shutdown, followed by another one.

“We want to try to do all the construction at the same time to minimize the period that we’re closed to the public,” she said.

“There’s a scenario where we could do the elevator, and then have the money for the [security] building come, and have to do that, and it would be a much longer closure period,” she said.

But it is unclear when the funding request, now before Congress, might be approved.

Del. Eleanor Holmes Norton (D-D.C.), the city’s nonvoting member of Congress, said in a statement that she would work “to help secure the funding . . . so that the dual projects can take place at the same time . . . [and get] the monument to reopen as soon as possible.”

The Park Service said the new facility will feature ballistic glass and screening equipment and will be able to handle 20 to 25 visitors at a time.

Kennealy said the monument may have the most heavily used elevator in Washington.

“Our elevator runs, during the summer months . . . 13 hours a day, nonstop,” he said. “It doesn’t rest. . . . This thing is running constantly, the motor, the gears, the control system, the doors.”

The monument has had an elevator since it opened. The first was steam-powered and took 12 minutes to reach the top. The trip now takes 70 seconds.

The Park Service wants to replace the elevator’s 1990s-era computer controls, the door systems, cab lighting and ventilation, and cables, and study the idea of a cab that does not need a park ranger onboard. The powerful electric motor, which dates to the 1960s, is “a beast,” Kennealy said, and only needs refurbishing.

The situation “is a drag, at this moment,” said Brian D. Joyner, chief of staff for the National Mall and Memorial Parks. “But it will be better.”

Kelsey Snell contributed to this report.