State Rep. David Duke, the president of the National Assn. for the Advancement of White People and a former national Ku Klux Klan leader, qualified as a Republican candidate for the U.S. Senate. Duke paid a $900 qualifying fee and filed papers with the secretary of state in Baton Rouge, La., about 20 minutes after state Sen. Ben Bagert of New Orleans, the official GOP candidate. The two candidates are challenging Sen. J. Bennett Johnston, a Democrat who is seeking his fourth term in the Senate. All three will face each other in an open primary Oct. 6. If no candidate wins more than 50% of the vote, the top two will be in a runoff on Nov. 6. Duke has run second behind Johnston in virtually all polls so far.