YOU CAN'T LANCE a boil until it comes to the surface. Now David Duke, having nominated himself the angry head of the boil called racism in American public policy, has demanded that everyone look at the spread of the infection. Its breadth and depth dismay many observers, but there is no denying, finally, its evil essence.
Mr. Duke, a former Ku Klux Klan wizard, showed support nobodwanted to believe he had. Running against three-term Sen. J. Bennett Johnston, Mr. Duke siphoned away 55 to 60 percent of the white votes in Louisiana. That boosted him to 44 percent of the total, despite losing 3-1 in New Orleans. Blacks in the state's biggest city, 55 percent of the voters, joined with whites who hadn't lost their heads to put paid to his Senate ambitions.
If a message was sent to Senator Johnston and others in politics, another message should be read by all those willing to bend to the wind blowing from the people fighting for the right to be unreasonable. It has multiple parts.
Part I has to do with who David Duke is and what he saying. National Republicans, and quite a few Louisianans, are deeply disturbed that a man with Mr. Duke's background would take up their banner. But those who say they reject his racist appeals have themselves succumbed to appeals inherently as racist if smoother sounding.
Ronald Reagan rode out of ''Death Valley Days'' into the California governor's mansion demanding an end to legal services for the poor, deep cuts in welfare programs and repudiation of the rebellion of the 1960s, a rebellion started by blacks.
The national Legal Service Corporation, through its local arms, helped whites as well as blacks. It helped -- and still helps, despite annual attempts to destroy it -- downtrodden people of any race, and its work in the Imperial Valley particularly nettled California land owners. Mr. Reagan took his opposition into the White House, on the way persuading many whites that fairness for the downtrodden was unfair to them.
Welfare has become a code word for blacks to many whites, despite the facts that most blacks have never been on welfare, that whites always outnumber blacks on the rolls and that the blacks who do need welfare want desperately to get off it and stand on their own.
But such facts have never stood in the way of prejudice. Thus, Mr. Reagan's mythical Welfare Queen struck a resounding chord in the hearts and minds of people who wanted to forget the critical needs social programs were created to serve. Should there be any surprise that David Duke travels the same ground, albeit in a more brazen manner?
Mr. Duke is a Nazi admirer who ran for president two years ago, fabricated a heroic record in Southeast Asia and had his face rebuilt by plastic surgeons. He scares many well-meaning whites. What if a less obviously bigoted demagogue said the things he says, with a smoother, more palatable approach?
Blacks, however upset over the ''below-the-radar'' support Mr. Duke has shown, have to view that question with cynicism. What was the Willie Horton campaign but a racist appeal, couched in terms that permitted whites to pretend it had something to do with moral rectitude?
The real question, as a Sun editorial noted, is whether George Bush can now dissociate himself from the overt bigotry Mr. Duke represents. Mr. Bush, who served eight years in the Reagan White House, has continued that administration's hostility to affirmative action. He might like to differentiate his opposition from David Duke's but Mr. Duke, a Republican despite all repudiation, makes that difficult.
Mr. Bush's test is shaping up: Congress, prodded by an electorate that includes growing percentages of the blacks, Hispanics, Asians and women whose push for broader societal participation upsets David Duke, already defied Mr. Bush with House and Senate versions of the Civil Right Act of 1990.
Mr. Bush has threatened to veto the final bill, which will upend the judicial activism of Chief Justice Rehnquist and his right-wing Supreme Court cohorts, but to do so puts Mr. Bush squarely in league with the former Grand Wizard.
It costs you something to do what's right. David Duke has not demonstrated the ability to be an effective state legislator. He survives politically because he says what many whites want desperately to hear, however: It's OK to be unfair if it keeps you No. 1. But the demographics of this ever-changing society say that the bad old days of racially defined exclusions and inhumanities will never come back again.
That's hard for supporters of David Duke to accept, but any other conclusion leads to a cataclysm no thinking American would willingly countenance.
And lest anyone forget, the Voting Rights Act insured that the Louisiana blacks who heard Mr. Duke's message of hatred, a quarter of the state's registered voters, had their say, too. It reads, ''No, Mr. Grand Wizard Swastika-wearer. You cannot ignore our rights and needs, ever again.''