RFR Realty has put 980 Madison Avenue, a low-rise commercial building that it owns on the Upper East Side, on the market. The squat, 100,000-square-foot property that stretches the full block between East 76th and 77th streets has both retail and office space, much of which caters to art galleries, including the well known Gagosian Gallery. Aby Rosen, RFR Realty’s chief executive, once had big plans for the limestone clad property. He went so far as to hire award-winning British architect Norman Foster to design a soaring glass tower that would rise from its roof and house high end apartments. When that plan drew community opposition, Mr. Rosen and Mr. Foster drafted a more subdued alternative, a mere five-story expansion. Later, when the recession struck, Mr. Rosen appeared to shelve his efforts to build residential space at the property. And in 2011, it even appeared as if he might be forced to default on his loans, when gallery tenants did not to renew their leases. Sources say Mr. Rosen has ironed out the building’s financial issues, but may now be seeking to take advantage of the city’s hot sales market, which has drawn many owners to put their properties on the auction block in recent weeks. Office buildings in prime locations in Manhattan have been selling as high as $1,000 per square foot. The sums paid for residential space and retail storefronts on busy corridors like Madison Avenue have been even higher. As a result, sources said 980 Madison Avenue could be worth $100 million or more, and the price could go even higher for a buyer confident in its ability to push a successful residential addition past the community. CBRE Group Inc. investment sales brokers Darcy Stacom and William Shanahan are handling the property’s disposition for Mr. Rosen.