... Obama is set to lay out his vision for advancing toward a world free of nuclear weapons during a speech Wednesday at the historic Brandenburg Gate in Berlin. A senior administration official says Mr. Obama will propose the United States and Russia cut their number of strategic nuclear warheads by up to one third below the level agreed to in a 2009 treaty. That pact, called the New START agreement, calls for the two countries to reduce their arsenal to 1,550 deployed strategic warheads by 2018.