For more than a decade, only poplar trees have grown between the stacked cinder blocks and rusted sheet metal on a 28-acre tract in the South Bronx. But suddenly the Oak Point garbage dump on the East River, abandoned in 1990 under a tangle of lawsuits, talk of mob ties and $60 million in debt, is sprouting with plans. The city wants to put jails there. The community hopes for an industrial recycling facility. But by far the most ambitious scheme for the land is a 1,075-megawatt power plant, big enough to provide the Bronx with all the energy it needs while also supplying about one-tenth of the energy needed to meet New York City's total demand.