Book excerpt: Myron Magnet's The Dream and the Nightmare argues that the radical transformation of American culture that took place in the 1960s brought today's underclass - overwhelmingly urban, dismayingly minority - into existence. Lifestyle experimentation among the white middle class produced often catastrophic changes in attitudes toward marriage and parenting, the work ethic and dependency in those at the bottom of the social ladder, and closed down their exits to the middle class. Texas Governor George W. Bush's presidential campaign has highlighted the continuing importance of The Dream and the Nightmare. Bush read the book before his first campaign for governor in 1994, and, when he finally met Magnet in 1998, he acknowledged his debt to this work. Karl Rove, Bush's principal political adviser, cites it as a road map to the governor's philosophy of ''compassionate conservatism.''