Gov. Rendell and Mayor Nutter were expected to announce the move today.
Details of the plan, including which parts of the Gallery site would host the slots machines and whether the existing buildings would be demolished, couldn't be determined last night.
The proposed move is good news for Delaware River communities who've opposed the Foxwoods site.
"This is a major step in the right direction," said Rene Goodwin, a Pennsport activist and member of the Philadelphia Neighborhood Alliance, which has opposed the two riverfront sites for slot parlors.
"The sooner they relocate, the sooner they can get up and rolling and start generating revenue," she said.
The SugarHouse casino also faces opposition at its current site, Delaware and Frankford avenues, but no alternate plans have surfaced.
The Gallery was developed with government assistance in the 1970s and '80s. The buildings were designed with three rooftop "pads" to accommodate a hotel and two office towers that could be built on top of the retail space.
A slots parlor on Market Street would likely present traffic challenges, but the Gallery is situated at one of the most ideal sites for public transit in the region.
It sits atop the Market East station, connecting it to all of SEPTA's regional rail lines, and is next to stops for the Market-Frankford elevated line and the New Jersey PATCO line.
DiCicco said that he'll be meeting today with representatives of Center City communities, including Chinatown and around Washington Square, who are sure to have concerns about the site.
DiCicco said that he's frustrated that he has no details to give constituents about the plan.
"There will be challenges involved, and I'll be asking some hard questions to make sure the people I represent are protected," DiCicco said. "But I won't be an obstructionist. I'll have an open mind."
Building Trades business manager Pat Gillespie said last night that the move makes sense. "We need these casinos, and if Foxwoods wants to move to the Gallery, that should satisfy everyone," he said.
The Gallery is owned primarily by the Pennsylvania Real Estate Investment Trust, whose chairman and chief executive officer is Ron Rubin. The Rubin Family Charitable Foundation is an investor in the Foxwoods project.
Foxwoods officials declined to comment last night on the proposed move.
It's unclear if or how Foxwoods would be compensated for its investment in the Delaware waterfront site, which the company has said exceeds $100 million. *
Staff writers Chris Brennan and Bob Warner contributed to this story.