The similarities between the War in Viet Nam and the War on Cities are instructive. We are now in the thirteenth or whatever year of the foreign involvement, and the third or perhaps thirtieth of the domestic crisis. Each entanglement somehow crept into being without any great attention being paid it by the general public. Each, of a sudden, has become acute in the eyes of government. After great exertions, ever greater ones are asked. The principal difference at this moment is one of phasing: among the public few would deny the reality of the Viet Nam situation, but as yet the idea that there is an identifiable urban crisis remains pretty much confined to specialists, or to spokesman for those groups, principally ethnic minorities, who might expect to gain most from a serious national commitment to the proposition.