By carving a large “donut hole” into the center of the existing Martin Luther King Memorial Library, the building could be an exemplary 21st-century main library space, full of light, open to multiple uses, easy to navigate and worthy of “a great city.”

Meeting on Wednesday night in special session in the main atrium of the rigorously modernist building — which is a study in right angles, rational layout and long vistas — the library’s board heard proposals for how to renovate the dilapidated steel-and-glass icon. Ideas included adding two more floors to the existing four, renting space to other tenants, converting below-ground levels to commercial parking and adding a cafe space under its stern, classically inspired loggia.

At stake is the future of one of the city’s most important examples of mid-century modern architecture, designed by Mies van der Rohe in the late 1960s — his only work in Washington, and his only library. The meeting advanced a process that began in November, when the library asked the Urban Land Institute to study its historically landmarked main building and consider all possible options. Among the possibilities on the table was to sell the structure and find a new home for a purpose-built main library branch.

But Wednesday night’s meeting suggests that the library is seriously considering the option of staying in its flagship, albeit with a major retrofit.

Library Board President John Hill said the purpose of the meeting was simply “to foster a discussion about the future of the library” and that no decisions would be made. But District librarian Ginnie Cooper said she had asked the library’s architect of record, the Freelon Group, to build on ideas that emerged from the ULI report and to consider the question: “Is a knock-your-socks-off library possible?”

Freelon came back with two basic architectural plans, both of which require cutting a large light well into the center of the rectangular structure. One design would criss-cross that space with stairways and bridges to create more open and dynamic floors. The other would emphasize the verticality of the new light well, with a glass-walled auditorium fronting onto a soaring central atrium. Both designs would keep much of the ground floor essentially intact — a requirement of the building’s historic preservation status — but would add stairs to allow patrons to circulate without using elevators.

Both designs include substantial renovation of the library’s systems, in many cases the same ones in place since it opened. That includes $12 million to replace the exterior glass windows — which, Freelon head Phil Freelon said, “waste energy to an appalling degree” — and $3 million to give the metal framing a fresh coat of paint, its first in 40 years.

Although, aesthetically, the library was thoroughly modern when it opened, many elements — including the light fixtures under the ground-floor loggia — are now antiquated: Bulbs burn out every six months, and replacing the entire system with something more efficient would cost more than $100,000.

The board also heard from real estate analyst Jair Lynch, who put some rough figures on the various options now before the board. Simply renovating the library as is, without the internal reconfiguration, would cost the District $5 million to $10 million a year in regular maintenance and upgrades. The plans presented by Freelon would cost between $175 million and $250 million. That could require an increase in the District debt limit, and could be a hard sell with the D.C. Council and voters. But other options, including a state-of-the-art automated parking facility below ground, might bring in new revenue, as would renting space on new floors added above the existing library.

The “dream big” approach of Wednesday’s meeting was probably intended to generate momentum toward solving one of the District’s most fraught architectural sagas. The Martin Luther King building is widely respected among architecture enthusiasts, and the city designated it a historic landmark in 2007. But despite new enthusiasm for the mid-century modern look, and concerted efforts at more consistent maintenance in past years, it isn’t universally loved. As Freelon acknowledged, if the library site at Ninth and G streets NW were bare ground, he could build a new bells-and-whistles library much more cheaply than remaking the old one.

Since at least 2000, when a team from the Washington chapter of the American Institute of Architects drafted a study for adapting the library, the city has studied, dithered and delayed finding a solution to the building’s long-standing maintenance and design issues. In 2006, then-Mayor Anthony A. Williams (D) pushed hard for moving the library to a new home on the site of what was once the old convention center, but he couldn’t sell the idea to the council.

In recent years, the old main branch has come to seem even more forlorn as the library moved forward with innovative and critically acclaimed new branch libraries and renovations. This year, Canadian newspapers published a “letter from Washington” detailing the sad state of the Martin Luther King branch and the role it plays in providing basic shelter and service to the homeless.

The plans presented by Freelon are, Freelon said, “only ideas.” But they are moving the library in the right direction, first and foremost, by keeping it in its existing home.

D.C. Council member Tommy Wells (D-Ward 6), who chairs the committee that oversees the library, attended Wednesday’s meeting and was pleased that the library was thinking about ways to remake the building. “What I like about it is they have met the challenge of making this building an exciting place for a new library,” he said.

Freelon’s team acknowledged the many legal and economic obstacles to its plans, including questions about what will be acceptable given its historic landmark status. Without mentioning specifics, David Maloney, the State Historic Preservation officer for the District, acknowledged that keeping the library in its current home was “a preservation plus.”

“There will certainly be a lot of discussion about it,” said Maloney, who also attended the meeting. But he says preservationists are aware of the challenges faced by the library and “will go into it with an open mind.”

Both plans presented by Freelon will raise serious philosophical issues about what is essential to the Mies design. A set of historic preservation guidelines — drafted by the library with input from the D.C. Historic Preservation Office and other key preservation groups — emphasized several essential “Miesian” elements that should be preserved, including the building’s horizontality, its symmetry and transparency. But it also stressed the need for advanced technology, sustainable design and an update of the basic programmatic needs of the library.

Mies’s design structured the interior, which was meant to be flexible and adaptable, as a series of five-foot modules and 30-foot bays, with shelving and reading tables laid out in an orderly march of regular units. Freelon’s vision argues for a more flexible internal layout, more reflective of the complicated webs and interconnections of the modern knowledge economy. Preservation purists might argue that Freelon’s design will simply preserve a Mies facade around a radically different internal aesthetic.

But the more intriguing of Freelon’s two programs, the one that stresses a vertical central atrium, exposes the rationalism of Mies’s design almost like a slice through geological layers of rock. It emphasizes the rectilinearity of the original structure while allowing a more flexible adaptation of the space.

The argument will come down to how deeply one channels the basics of what Mies was after. If underneath the modules and bays was a more profound desire to give easy, direct access to knowledge, then Freelon’s design re-creates Miesian ideals in a new language. If one believes he worshipped the grid for pure aesthetic appeal, then the new designs might seem to do violence to his ethos.

The positive news, however, is that the library wants to have a conversation about staying in its historic home and isn’t planning to set sail for a new one. That would keep the library in a revitalized neighborhood, near two major Smithsonian museums, two central axes of the Metro system and the mushroom field of new buildings rising on the old Convention Center site.

It would keep the library at the symbolic center of the city, which is right where it should want to be.