THE rise and fall of David Duke was more evidence of the polarization of American voters along color lines - supporting what the Kerner Commission found in 1968: "Our nation is moving toward two societies, one black, one white - separate and unequal."Mr. Duke was resoundingly defeated. But this former Nazi and Ku Klux Klansman still picked up 55 percent of the white vote in Louisiana and 56 percent of the GOP vote. At the same time, just about all of the black vote was cast for Duke's opponent, Edwin Edwards, who had twice been tried and acquitted on federal racketeering charges. Most of Mr. Edwards' supporters viewed him simply as the lesser of two evils. The intense racial hatreds that erupted in the 1960s are no longer apparent. Tensions have eased markedly. Many blacks have been able to attain upward mobility - at least economically. And some blacks have been rewarded with stunning success in public life - for example, Virginia's Gov. Wilder, New York's Mayor Dinkins, Los Angeles' Mayor Bradley, Cabinet Secretaries Sullivan and Pierce, and former House Majority Whip William Gray. And one can't overlook two high-level black appointees: Colin Powell and Clarence Thomas. The result in Louisiana can be seen in a positive light, so far as race is concerned. It was not too many years ago when blacks in the South either were disenfranchised or discouraged from voting because of a poll tax or other impediment. Some predicted blacks wouldn't exercise their right to vote even after the way was opened to them. Some evidence of a slowness to vote has been found among blacks. But it was often because the choice of candidates gave them little reason to go to the polls. When the choice meant something, they voted. Just look at Louisiana! About 80 percent of eligible blacks (the same percentage as whites) poured out to keep a politician they perceived as their enemy from winning. Let no one ever again underestimate the eagerness of blacks to vote if they perceive the result as meaningful to them. Yet a tendency among blacks to vote as a block - almost always, since the days of Franklin Roosevelt, for a Democratic candidate - is itself a polarizing factor, one often ignored by the pundits. It's natural for many blacks to vote that way. To the older generation, FDR was seen as a savior; Presidents Kennedy and Johnson were viewed as heroes and friends who championed the civil-rights cause. The white vote is being described as angry or hateful in its opposition to black progress. Some of it is. But much of that resentment rests on economics: Many whites, who don't view themselves as being anti-black, feel that the cost to them of black progress is intolerably high. By this, they mean their tax burden. At base, of course, is fear and misunderstanding. Democrats charge that Republicans use code words like "family values" and "affirmative action" to stir up these emotions among white voters. Republicans, led by George Bush, say these words relate to issues that actually confront the nation. In any event, the dividing up of black and white voters, particularly in their choice of president, has clearly given the Republicans an advantage - simply because there are more white voters. The GOP presidential candidate has won the white vote in every election since FDR - except in 1964, when Lyndon Johnson drew a majority of whites in his race against Barry Goldwater. The 1988 presidential election showed President Bush doing exceedingly well among whites, especially in the South where he won 68 percent of the white vote and only 12 percent of the black vote. In the Midwest the white vote for Bush was 57 percent and the black vote only 8 percent. A generation has gone by since the Kerner report. Black Americans have progressed in many fields of endeavor. Legislation has helped blacks immensely. I'd like to believe we are no longer "moving toward two societies, one black, one white - separate and unequal." But the Duke-Edwards race did not reassure me - even though I hailed the result.