The District’s historic main library could have a future as a mixed-used building, sharing space with a tenant who would help the city tap some of the value in the structure designed by Ludwig Mies van der Rohe.

Whatever the District decides to do with the Martin Luther King Jr. Memorial Library, it had better decide soon, a panel that recently assessed the 40-year-old building said Friday.

Poor conditions in the building — including problems with the ventilation system, outdated elevators and asbestos — need to be addressed, the panel of experts in architecture, urban planning and development said.

“This building is not in good condition, and it needs help,” said Wayne Ratkovich, chairman of the Urban Land Institute’s library advisory group. The library system, in partnership with the Downtown Business Improvement District, commissioned the institute to assess the value of the property, which is designated a historic landmark by the D.C. Historic Preservation Review Board.

“It probably shouldn’t be delayed for five years while decisions get made,” said Ratkovich, a Los Angeles-based developer.

Renovations to the landmark at G and Ninth streets NW could cost up to $250 million, according to a city study the panel cited.

The panel said the city could:

●Share the 440,000-square-foot space with another tenant, possibly a school, a nonprofit group or a museum. City officials estimate the system needs only 225,000 to 250,00 square feet for the library. Leasing space could generate $4.1 million to $5.5 million in annual rental revenue, which could be used to fund a portion of the rehabilitation.

●Sell the property and move the library to a city-owned location. The city could generate $50.8 million to $70.5 million from a sale that could be used to construct a new building.

“We understand and we feel really the emotional ties with regards to this building. . . . However, in order to be able to stay in this building as a sole occupant, there has to be a commitment for at least, according to [the city’s] own study, $200 million to $250 million,” said Ayahlushim Getachew of Thomas Properties Group, who was a member of the panel.

She added that the financial requirement seems unrealistic given the city’s finances.

The panel, which did not endorse a recommendation, also discussed redeveloping the building to add more floors and amenities, such as a rooftop terrace, a cafe and more underground parking. The experts plan to release a final report in 60 days.

Richard Layman, who blogs about urban planning in the District, said he hopes the library stays at its current location, where there is “this incredible energy.”

“You got the Verizon Center, you have the museums . . . you have the convention center. There is this renewed energy — continued energy — and why shouldn’t we say that the civic is important, not just the commercial?”­­

The facility’s poor conditions and the needs of modern library service have been subjects of debate for years. Former mayor Anthony Williams’s administration considered building a new library a block away, at the old Washington Convention Center site.

Ginnie Cooper, the District’s chief librarian, said staying at 901 G St. NW is preferred.

“The building is 40 years old, and it’s had lousy maintenance,” she said. “I mean, we haven’t been able to replace the boilers or modernize the elevators or deal with the asbestos in the building.

“I hope the mayor and the elected officials recognize that whatever happens we need some big money to be able to address those underlined systems that are in such trouble,” she said.

Then, looking at children in the library, she said, “I hope the conversation turns on how to make sure that when those kids are in junior high, we have . . . a modern library able to meet their needs.”