A consideration of what arms limits upon the United States and the Soviet Union are desirable. That a ban upon both MIRV and ABM systems would stabilize the bipolar strategic balance, and slow nuclear proliferation, is disputed. A MIRV ban would encourage thick ABM defenses of cities, and could easily be evaded by the Soviets. Expected superpower postures with MIRV and thin ABM systems will, with low-cost marginal adjustments for protection against "nth" powers, markedly increase the costs of acquiring retaliatory capabilities against a superpower. Many nations will use such arming rather than disarming by the superpowers ("vertical proliferation") as an excuse for not signing the Non-Proliferation Treaty. But the number of nuclear powers should expand no faster, while the ambitions of nth country strategic programs should expand more slowly. 26 pp.