Americans, says this writer, have continued faithful to an image of Europe conceived immediately after World War II--despite the fact that this image bears no relation to contemporary political reality. New basic assumptions are necessary, Mr. Lerche insists. His book therefore has a dual purpose: to present a general picture of Europe as it actually is today, and to promulgate the fundamentals of a feasible policy. Required first of all is the admission, by the U.S., of the concept of fully equal partnership. Secondly we have got to acknowledge that Europe, if it agrees on anything, is united in an insistence upon a detente with Soviet Russia. Acquiescence on these points, Mr. Lerche suggests, would be much more of a gain than a loss--it would free us to maintain our interests in the rest of the world. Partnership should extend to economic as well as political matters; the developed nations should freely compete and by so doing seek to complement each other, to the natural benefit of all concerned. In the recent deluge of books on such questions, Last Chance in Europe stands forth as one of the frankest and most readable, if not the most comprehensive.