When you’ve flooded the economy with trillions of dollars, mopping up is no easy task. That’s the reality the Federal Reserve is confronting as it starts to explain how it will undo the aggressive growth-supporting steps that were put in place when the economy was in its deep dive — and begins to be clearer about when that may happen. But it is a fraught exercise. Federal Reserve leaders and private economists expect the jobless rate to remain high for years, despite a dip in the unemployment rate to 9.7 percent in January, and the Fed could make the situation worse if it moves too abruptly.