FERRIDAY, LOUISIANA. — DON'T BE TOO surprised if Louisiana sends a former Grand Wizard of the Ku Klux Klan up to the U.S. Senate this year. ''Good ideas. Bad background'' seem to be the code words white Louisianans use in telling Yankee reporters and pollsters that whether or why they vote for David Duke is none of your business.
Polls say Mr. Duke, a charismatic young man who was elected as a Republican last year to the state legislature, will get only about 30 percent of the vote against Sen. J. Bennett Johnston, the Democratic incumbent. But even on Bourbon Street in New Orleans, much less in hot, flat, small towns like this one, hometown of Jerry Lee Lewis and Jimmy Swaggart, you can't find many people ready to put up their own money to bet those odds.
No one, pollsters included, is sure what will happen behind closed curtains in the state's voting booths on October 6. (Louisiana has an open primary in which all candidates, regardless of party, run together in a first round. If a candidate wins more than 50 percent of the vote, that's it. If not, the top two candidates face each other again November 6, the day the rest of the states choose senators and congressmen.)
The ideas of David Duke that white folks say they like are these: no new taxes, ever; a flat income-tax rate of 8 to 10 percent for all, no matter what their income; make welfare recipients work for benefits and cut off all aid to persons testing positive for drugs; abolish all affirmative action and minority set-asides in hiring, promotions, contracts and scholarships.
The background is wacky, at least by my standards. But, ideology aside, Mr. Duke does have the almost manic intensity of many men and women who make good for a while in American politics.
He has packed a lot into his 40 years. He was wearing a brown shirt and the swastika as a teen-ager in 1970, picketing civil-rights workers, and quickly became well known for white supremacist and anti-Semitic speeches at Louisiana State University. He joined the Klan at 22 and became Grand Wizard at 25. He is the founder of the National Association for the Advancement of White People and the author of strange books about sex and street-fighting. He sold books from his legislative office, including one called ''The Hitler We Loved and Why.''
''The same kind of courage it took to do what I did then is what drives me in what I do now,'' he told Mark Coomes of the News-Star of Monroe. ''There are a lot of things I regret. I've made some real mistakes, but I've changed my mind and grown up on certain issues.''
It is not exactly clear from the campaign, however, just what has changed in the mind of David Duke. But Americans, bless them, do not dwell on the past, even when they should. ''Ye without sin cast the first stone,'' said Curt Maddox, a retired disc jockey introducing Mr. Duke at a picnic the other day. ''The Bible doesn't say God forgives everybody but David Duke, now does it?''
''I recently read in the newspaper that Sen. Johnston would get the vote of the upper class,'' wrote M.M. Rhodes of Farmerville to the News-Star. ''I do not intend to vote for Johnston. Does this indicate I am of the lower class? . . . He has run his campaign on Mr. Duke's past. What about Johnston? Where was Mr. Johnston when our state was becoming stagnant? Where was he when the S&Ls went sour?''
Mr. Rhodes is mad. Voters are angry -- again. Mr. Johnston, chairman of the Senate Energy Committee, may be in the wrong place at the wrong time. And Mr. Duke will be in the wrong place for the national Republican Party if he fast-talks his way to Washington. Jesse Helms will look like Woodrow Wilson compared with this guy.
My guess is that Mr. Duke will win a majority of the white vote, certainly the white males. If Senator Johnston survives, it may be only because of Saddam Hussein driving up oil and gas prices in energy-rich Louisiana, and the fact that almost 30 percent of Louisiana's voters are black -- which, of course, is one reason the state's best-known racist could get this far this fast.