Treasury Secretary Timothy Geithner on Tuesday defended the government’s rescue of American International Group Inc (AIG.N) in September 2008, saying the action was necessary to prevent the country from plunging into a possible second Great Depression. Geithner’s comments came in testimony he provided in the trial of a lawsuit brought by Hank Greenberg, AIG’s top executive from 1968 to 2005, who contends the terms of the government $85 billion loan to AIG cheated its shareholders.