Ross campaigns outside Leon Electric Building: The mayoral candidate pushed for city re-development to focus on neighborhood targets like this prominent Uphams Corner warehouse next to the Fairmount Line. Photo by Gintautas Dumcius

A day after state Rep. Marty Walsh, a mayoral candidate, proposed moving City Hall as part of a plan to revitalize Government Center, a rival called the idea “stale” and said the next mayor should be focused on areas like Uphams Corner and its Leon Electric Building, a neighborhood eyesore.

Walsh on Sunday unveiled a proposal to sell off City Hall Plaza, putting it back on tax rolls to the tune of $10 to $12 million a year, creating construction jobs, and netting an estimated $125 million to $150 million in onetime revenue. The city would then ask a private developer to construct a new City Hall, which the city would lease until it would eventually revert back to the city at the cost of $1. Walsh said the revenue would be used to fund universal early childhood education, parks, public art and add to the city’s rainy day fund.

But District 8 Councillor Michael Ross, who is also running for mayor, said on Monday the proposal was nothing new, and this was the “fifteenth time” he’s heard the idea during his 14 years as the councillor for District 8, which includes Mission Hill, Fenway, Beacon Hill, the West End and Back Bay.

Mayor Thomas Menino has previously proposed moving City Hall to the Seaport area of South Boston, but backed off the plan after opponents raised concerns that it would the seat of city government less accessible, since the plaza is currently on top of the Green Line, the Blue Line and the Orange Line. Walsh said that his plan is different and he plans to keep City Hall in the downtown area.

Walsh and Ross join 10 others on the Sept. 24 ballot. The preliminary that day will winnow the field down to the top two vote-getters.

After calling Walsh’s plan “stale,” Ross pivoted to his plan to create 10,000 units of housing along the Fairmount Line, which stops just outside the Leon Building — a high-profile warehouse complex on Dudley Street that is a prime target for re-development.

“The next mayor can’t just be focused on building big buildings and downtown development,” Ross said at a press conference on Monday morning, across the street from the building. “Those are important. But the next mayor needs to be focused on growing our neighborhoods and building more transit-orientated development and affordable housing. That is how we will slow skyrocketing rents and home prices.”

Ross noted that the Leon building had been “eyesore and a drain on the community” for years, since the owner has rebuffed efforts to engage in conversation with city officials, and it is a “prime candidate” for a mix of retail and residential buildings.

Separately, Ross sent a letter to the owner of the Leon Building, Arthur Leon, hinting that as mayor he would be willing to take the property by eminent domain, similar to a recent City Hall land-taking on Washington St. in Roxbury.

“As Mayor, I would make improving this site one of my key priorities and will not hesitate to look at similar situations, such as on Washington Street in Dudley Square, and use that as a precedent should you be unwilling to engage in a conversation about your building,” he wrote. “The potential for improvement to this space is tremendous and one that the city cannot afford to let go unused for any longer.”

In a phone interview with the Reporter, Walsh defended his plan to move City Hall, saying it would “rejuvenate” the wind-swept Government Center and connect Faneuil Hall with Cambridge St.

“I haven’t heard any criticism from the average person on the street,” Walsh said.

Walsh added that he has played an active role in the Dorchester community and Uphams Corner in particular, as a member of the Dorchester delegation on Beacon Hill.

“I haven’t seen Councillor Ross here,” Walsh said. “I’ve certainly been working there as a state representative.”

In response to last month’s Reporter survey of all the candidates that included a question about what they would do with the Leon Building, Walsh said the site could be reused as space for artists, a small business incubator or mixed-income housing, while the adjacent outdoor space could be a “neighborhood plaza for events.”

Walsh’s City Hall plan also came in for some criticism from Mayor Menino, the corner office’s current occupant. He called the plan a sign that the campaign was in full “silly season” mode.

“Come up with great ideas,” Menino told reporters during a visit to Fields Corner’s Harbor School, according to the State House News Service. “I’m not getting involved in the campaign, so Representative Walsh makes his statements and we’ll see how far it takes him,” Menino added.