CHAIN REACTION: THE IMPACT OF RACE, RIGHTS, AND TAXES ON AMERICAN POLITICS. By Thomas Byrne Edsall and Mary D. Edsall, W.W. Norton, 339 pp., $22.95IF a single image could get to the nub of modern national politics, as Thomas Byrne and Mary Edsall see it, it would have to be Willie Horton. The Massachusetts convict committed a rape on a weekend furlough from prison, then 1988 Bush campaign commercials made him an infamous symbol for liberal attitudes toward crime. A legitimate question of values lurked around Mr. Horton and his furlough. But both political parties managed to evade it. The Republicans used Horton like a match to inflame a whole set of concerns about social values - concerns shaped by images of race. Horton, after all, was not just incorrigibly criminal, he was black. The Democrats responded with cries of "racism" and "irrelevance," but failed to look the deeper social concerns coldly in the eye. The rest of the story is, of course, that the Republicans won. They will keep on winning at the highest levels, the Edsalls write in their even-handed book, until the Democratic Party faces up to some hard moral and cultural questions about what works in fighting poverty and crime. Until then, for key groups of white American voters, concerns about work, family, community, and morality will remain bundled up with images of race. Thomas Byrne Edsall, a Washington Post political reporter, and his wife, Mary, a short-story writer, describe a new incarnation of an old theme in American politics. The venerable political scientist V. O. Key wrote at mid-century how whites of modest means in the deep South supported the rule of the planter aristocracy - against what Professor Key saw as their own better interests - rather than share power with blacks. The Edsalls revive Key's thesis to explain the pass at which national politics has arrived in the post-civil-rights era. Working- and middle-class whites join the affluent in voting Republican - against what the Edsalls see is their own best interests. Race is again in the middle of it. The rights revolution that began a quarter century ago opened the doors to equality and fairness for many new people, notably blacks and women. The costs of this rights revolution have been borne disproportionately by lower-middle-class whites "who frequently competed with blacks for jobs and status, who lived in the neighborhoods adjoining black ghettos, and whose children attended schools most likely to fall under busing orders." These were many of the voters who found the newly established rights of accused criminals, abortion rights, and bans on school prayer most difficult to comprehend. The very working people who most benefited from the federal programs under the New Deal began thinking of themselves as taxpayers and others - blacks - as tax recipients. Even though by 1980 most black Americans were themselves middle or upper-middle class, white perception centers instead on the underclass - riddled with crime and drugs, prom iscuous, welfare-supported, and nonworking. Modern Republican politics is no return to Key's Jim Crow South, in the Edsalls' view. Overt racism is no longer acceptable to vast majorities of Americans. But blacks have become a symbol of social disorder for many whites. The Edsalls blame the Democrats for willfully ignoring the values-race tangle as much as they blame the Republicans for exploiting it. Concern over being charged with racism and blaming the victim long kept Democrats from confronting issues such as the deterioration of the black family. This book is not written for popular audiences, but it is important because it hoists understanding of the politics of race to a new level where the view is clear and the blame more complicated. Yet it remains hard to believe the Edsalls are not inflating a little the power of race. The best news is that a strong contingent in both the Democratic and Republican Parties are plying the very ground the Edsalls are pointing toward and are working toward decoupling race as a symbol and social disorder.