QUINCY — Mayor Thomas Koch announced plans Monday night to speed up development of the New Quincy ­Center and offered new ­details about an area called ­Merchants Row.

Steel will be going into the ground by February or March 2013 for Merchants Row, a $120 million development that includes two residential lofts, office space, retail space, and a renovated Granite Trust building at 1400 Hancock St.

The space will go in the exist­ing Fat Cat parking lot and take over the block of buildings bounded by Hancock Street, Chestnut Street, and Cottage Avenue.

Development of Merchants Row will occur earlier than previously planned and would take place before any of the other planned development of the downtown, which is set to begin in fall 2013.

Those plans, which include the development of anchor retail space and street retailers in the easterly portion of the downtown development, will remain on the existing track despite the change.

According to Paul Hines, assistant city solicitor, the major milestones of the project do not change, and there will be no amendments to the city’s contract with the city’s developer, Beal/Street-Works.

Merchants Row is one part of an ambitious, $1.6 billion redevelopment of downtown Quincy, meant to bring in new office, retail, and residential space into the city’s center. The entire project could take 10 years.

Under the new development schedule, Merchants Row would be completed along with Adams Green, a renovated green space in front of Quincy City Hall that will connect the Quincy T Station to Merchants Row.

Richard Heapes, a managing partner of Street-Works, said his firm can speed up the Merchants Row portion of the project because the firm owns all the property and it is not affected by signifcant infrastructure needs.

“We can only do this because we own and control all of the property, and it is without a doubt the right thing to do for Adams Green to make all the work come up together,” Heapes said.

The city will still have to renovate and relocate the Town Brook, which must be finished before Street-Works starts developing the next section of the downtown, and must construct a Burgin Parkway Access Bridge.

According to Ken Narva, also a managing partner of Street-Works, it makes sense to bring up some private ­development along with the city’s major infrastructure renovations, and Adams Green must be completed along with the development of Merchants Row.

“We need it to come online at the same time,” Narva said. “Otherwise it’s a block floating by itself.”

Koch has asked for an endorsement from the City Council for the accelerated schedule.

The council referred the topic to committee and will vote on it in coming weeks.