A rendering of the redesigned Martin Luther King Library by three architecture firms. (Freelon + Studios Architecture; Ayers Saint Gross and Krueck+Sexton; Mecanoo and Martinez + Johnson Architecture)

The three architectural firms invited to submit proposals for renovating and possibly expanding the Martin Luther King Jr. Memorial Library in downtown Washington presented their ideas Friday to an invited audience at the National Building Museum. Saturday, they will do the same for a public audience at the library, and a decision on which team will be asked to do the project will be announced Tuesday.

One thing became painfully clear after the three presentations: Ludwig Mies van der Rohe’s original 1972 steel-and-glass box is fighting hard against assaults on its basic purity. None of the three teams has solved all of the problems: how to update it for more contemporary library functions while respecting the essentials of Mies’s architectural vocabulary, and how to expand it for other uses — possibly residential or office space — without making it seem a public plinth supporting a private addition.

When the D.C. Public Library began considering the possibility of adding space to the MLK Library building, there was a sense that this could be done fairly easily and with minimal impact on its austere, geometric presence. The original structure was designed with support columns sufficient for adding extra floors, and the simple facade of floor-to-ceiling windows framed by steel girders could be extended seamlessly, like adding extra lines to a grid.

But none of the firms chose the low-impact extension option. To different degrees, they all went architectural, over-thinking the project and freighting it with trendy conceptual forms that will likely never coexist comfortably with the original design. One can’t blame them entirely: The DCPL leadership wants the renovated library to do many things that Mies never envisaged, and the presentations Friday demonstrated that dragging the old building into the 21st century will be much more complicated than originally thought.

The best presentation, because it most respected the original architecture, came from the team of Patkau and Ayers Saint Gross, which stressed preservation of the original monumental lobby space and the essential box-like form of the exterior. The team would leave the basic form of the ground floor intact but add visually prominent escalators to solve the building’s most truculent problem: its lack of flow and connection between the floors. A cafe would be inserted in the grimy and depressing alley that separates the library from its new neighbor, 945 G St. NW (which includes a lovely church space by the New York-based Tod Williams Billie Tsien Architects).

The Patkau team leaves its biggest alterations for the top levels, where it would insert a “cloud” form that would contain a “dream lounge” and “media exchange; yet it isn’t clear how the team would fit usable space into this non-Euclidean bubble form.

If DCPL decides to add extra space to the building, the Patkau team proposes obscuring its three-floor bulk behind a screen-like extension of the facade that would be open to the air above.

The other two proposals are more radical. The team of Mecanoo and Martinez and Johnson Architecture would remove almost all of the interior brick walls, replace them with glass, and add glass elevators and prominent staircases to connect the building’s levels. If residential space is added, it would be an oblique form on top that would be visually distinct from the Mies facade. Francine Houben, of the Dutch firm Mecanoo, stressed the need for the space to be welcoming, and she seemed bemused by how old-fashioned much of the original design is today. She also stressed making the library more environmentally sustainable.

The team of Studios Architecture and the Freelon Group also proposes substantial changes to the ground floor, introducing a monumental staircase that suggests a circulation pattern leading from the city outside to rooftop gardens that would be added. A large auditorium would jut into a huge atrium space in the radically remade core of the building, and if residential units are added, they would be even more distinctly articulated, even overhanging the original building in one spot.

Both of these high-impact designs will likely leave the original building feeling a bit like a shell on the outside, with only shards of the original design left inside. There is a perfectly reasonable argument that when adding new forms to historic structures, it’s best to be honest and allow for a distinct juxtaposition of styles rather than trying through sleight of hand to join new and old seamlessly.

But it became painfully clear Friday that Mies’s library is an exception to that rule. Its modernism is too self-contained, too austere, too reticent, to survive a post-modern dialogue with something as jarring as what these teams have proposed. Patkau is the best bet, but even it has a long way to go.