Fannie Mae, the government-controlled mortgage-finance company, bought the loans Deutsche Bank Berkshire Mortgage made to Ocelot for 18 of Ocelot’s 25 buildings, totaling $29 million from 2006 to 2007. Fannie Mae has now acknowledged that the loans did not meet their underwriting standards at the time of origination.

Mr. Cestero said in an interview that the poor conditions created by overleveraged buildings were nothing like the widespread abandonment of the late 1970s and early ’80s, which turned some neighborhoods into urban wastelands. But he said the conditions not only threatened tenants’ health and safety, but risked destabilizing entire blocks. As a result, he said, the agency had become more aggressive in tracking the buildings, making emergency repairs and working with lenders to find new, responsible owners, as he said the agency was doing with Fannie Mae on the Ocelot buildings.

“We are very concerned and continue to be concerned about the overall problem that Ocelot represents in the city, where you have multifamily buildings in some state of financial distress,” he said. “If that financial distress is not corrected quickly, you will ultimately end up with physical distress.”

Tenants have grown frustrated waiting for repairs. Fannie Mae, which initiated foreclosure proceedings in March on the 18 Ocelot properties for which it had purchased loans, is able to make repairs only in those buildings for which a court has appointed a receiver. Residents at one run-down Ocelot building sued the landlord, persuading a judge to appoint an independent administrator to make repairs.

Ocelot, which described itself in a 2007 Deutsche Bank press release as building a portfolio of subsidized, “income-producing real estate,” has become a kind of phantom. Its Web site is defunct. It used to have a suite in a Madison Avenue office tower, but it was evicted this year for nonpayment of rent. “The owner is making no attempt to repair the buildings or fix the violations or make them decent places to live,” said Mr. Cestero, whose agency has so far paid for roughly $850,000 in emergency repairs in the 25 buildings, money Ocelot now owes the city.

Rachel Arfa, Ocelot’s president, did not return phone calls seeking comment.

For Ocelot tenants in the Bronx, life has been far from ordinary.

At 1744 Clay Avenue, residents have endured winter days without heat and hot water. The super has not been paid in about three months; tenants took up a collection to buy building supplies. At 2254 Crotona Avenue, the occupants of one apartment abandoned it last year after parts of the ceiling collapsed, leaving many of their belongings behind. It remains vacant, a small-scale disaster zone of leaky pipes and caved-in walls and ceilings. Tenants in the building and other Ocelot properties use knives and screwdrivers to open doors without locks or doorknobs.