Paul H. Nitze, an expert on military power and strategic arms whose roles as negotiator, diplomat and Washington insider spanned the era from Franklin D. Roosevelt to Ronald Reagan and helped shape America's cold war relationship with the Soviet Union, died Tuesday night at his home in Washington. He was 97. The cause was pneumonia, said his wife, Elisabeth Scott Porter. From the beginning of the nuclear age, whether in government or out, Mr. Nitze urged successive American presidents to take measures against what he saw as the Soviet drive to overwhelm the United States through the force of arms....