By LOUIS UCHITELLE Published: May 17, 2009 General Motors is engaged in negotiating a reorganization that could increase vehicle imports from its plants in Mexico and Asia while closing factories and cutting the work force in the United States. That approach drew a sharp rebuke from the United Automobile Workers union on Friday. In a letter to each member of Congress, the U.A.W., which represents G.M. factory workers, argued that to qualify for more government assistance, the auto giant should be required