As Beantown’s race for mayor heats up before the November election, the future of the controversial Kallmann McKinnell & Knowles–designed Boston City Hall hangs in the balance, yet again. The Brutalist-style structure was lauded by critics when it was first completed in the 1960s, but has received mixed feedback over the years. In 2006, Mayor Menino pushed for the relocation of City Hall to the Seaport District—an area in which he has been integral in ushering in a wave of new development. The plan, however, never materialized. And now one mayoral candidate, Representative Martin J. Walsh, is focusing his efforts on the revitalization of downtown Boston, and the demolition of City Hall is emerging as the linchpin of his plan.

Walsh has argued that the city sell City Hall Plaza to a private developer for roughly $150 million to construct a new mixed-use complex on the 4.5-acre site, likely consisting of residential, hotels, retail, and office space. Municipal Center would then be moved to a location in or around Downtown Crossing, Government Center, or the Financial District, to be owned and operated by another private developer for a 20 to 40 year period.

“A 21st century economy has emerged, and the new mayor must refocus the development to the core economic engine of the city, the downtown. This area must evolve from a 9-to-5 weekday, government-dependent culture, to a culture economically driven to add value 24/7 to surrounding businesses and neighborhoods,” said Walsh in a statement.

This proposal, Walsh has said, would generate significant revenue from both the sale of City Hall and new annual taxes, and would also provide a direct link to the Quincy Marketplace, which the candidate said has struggled since the Seaport became a popular destination.

But some of Walsh’s rivals have been quick to express opposition to his plan. Mayoral candidate and Councilman Mike Ross called the idea “stale,” and said that the priority needs to shift to creating affordable housing along transit nodes in neighborhoods throughout Boston.

“The citizens of Boston are hungry for bold new ideas, not just another conversation about moving City Hall. The next mayor can’t just be focused on building big buildings and downtown development,” said Ross in a speech outside the Leon Electric Building, an expansive structure for which he is proposing a mixed-use development.

The threat of demolition has also struck a chord with members of the architecture community. Several years ago, preservationists and local residents came together and formed the “Friends of Boston City Hall,” an advocacy group seeking to preserve and update the massive concrete building.

“It stands more than any other building for the renaissance of Boston in the 20th century architecture,” said David Fixler, president of Docomomo US/New England and partner at EYP Architecture & Engineering. “It was the catalyst of creating the Boston we know today, which is a world class city, which it wasn’t in the 1950s.”

Fixler points out that the building has its flaws, but believes that the city should conduct a comprehensive feasibility study to explore the options for renewing it.

“The building is not perfect, the plaza is not perfect. There are things we need to address and make more humane and friendly to the users. But the potential is there,” said Fixler.

Several recommendations have been floated to revamp the building and make it more useable, including implementing energy efficient strategies to lower the heating costs as well as transforming the plaza into a more lush, pedestrian-friendly space.

“Why not work with what you have, which is the sustainable thing to do and the culturally referential thing to do, and let Boston be an example of adaptive reuse,” said Fixler. “It is a building that more than merits that for the architectural community and the city of Boston as well.”

Whether or not the next mayor decides to relocate City Hall, change has already taken hold of downtown Boston. The area, which has been primarily a hub for business and government, is experiencing a surge of new residential development.

Developer Millennium Partners just broke ground this month on a new 625-foot residential tower next to the former Filene’s building in Downtown Crossing. Handel Architects has been hired by the developer to design the 450-unit tower as well as renovate the adjacent early 20th century landmark, designed by Daniel Burnham, and transform it into a multi-use complex with an upscale food market, retail space, and creative businesses.

“We are getting this landmark building back to its original concept—this palace of commerce—will now be a palace of creativity,” said Handel partner Blake Middleton.

As of now, the apartment tower will stand as the tallest residential building in Boston, and will include retail on the first three levels. The design took its cue from the “wonderful rectangular linearity to the facade” of Burnham’s terra cotta and steel frame building. Middleton said they also looked to the “simplicity that Cobb was able to conceive with the John Hancock building,” while “clearly establishing our own identity.”

Only a short distance from Downtown Crossing, Pei Cobb Freed & Partners along with Cambridge Seven Associates, just received the green light from the Boston Redevelopment Authority to build a set of towers in Back Bay. Once built, the 58-story hotel and condominium high-rise will top the Millennium Partners tower and rise to 691 feet to be the tallest residential tower in the city.

“The idea of the 24-hour city has really become a successful model. It really does take a particular mix of uses. The synergy of these uses has to be carefully calibrated,” said Blake Middleton.