NEW ORLEANS, OCT. 6 -- Renegade Republican David Duke, tapping into a deep well of racial and economic resentments among Louisiana voters, ran far stronger than political experts expected, but fell short tonight in his challenge for the Senate seat held by Democrat J. Bennett Johnston.

With 98 percent of the ballots counted, Johnston won reelection to a fourth term by polling 54 percent of the vote in an open primary against Duke and two minor candidates. Duke, the former Ku Klux Klansman who represents the New Orleans suburb of Metairie in the state legislature, picked up 43 percent, well above the figure most Louisiana political experts had assumed was his maximum pool of support.

Duke ran so strongly in the bipartisan primary that it appeared he would have forced Johnston into a November runoff had not the official Republican candidate, Ben Bagert, dropped out of the race two days ago in a last-minute effort by the GOP establishment to stop Duke, whose past ties to the Klan and associations with American Nazi Party figures were a source of embarrassment for Republicans.

Refusing to concede, Duke appeared before a rousing throng of supporters late tonight and said that he would challenge the election in court. He said that absentee ballots for Bagert -- ballots that the secretary of state announced would not be counted -- should be included in the total vote. Those votes, Duke said, might deny Johnston the majority he needed to avoid a runoff.

"We have not yet begun to fight," said Duke. "There were thousands of absentee ballots cast that are not being counted, and we'll fight to get them counted. We expect the next senator, whoever that person might be, to win by a true majority of the votes. Bagert's voters are being disenfrahnchised."

Johnston rejected Duke's complaint as "a silly charge."

Duke's showing was strong in all sections of the state, according to voting analyses. Loyola University political scientist Ed Renwick said it appeared that Duke was attracting 60 percent of the white vote. "That is a tremendous victory for him," Renwick said. "He's going far beyond what we thought he could get. This will only increase Duke's power."

Turnout was extraordinarily heavy throughout the state. Officials in Baton Rouge said the final turnout might exceed 70 percent, a record for an off-year primary election in Louisiana. By comparison, primaries in other states this year have averaged about 20 percent turnouts.

Johnston and his aides were subdued most of the night even as he was winning reelection. They had privately hoped that with Bagert out of the race, Johnston would win decisively, perhaps topping 60 percent. The best light they could shine on the night's events was to claim that Duke's showing was more of a problem for the Republican Party than for them.

In his victory speech at a downtown New Orleans hotel, Johnston expressed relief that he had survived what he called "a hard, tough, rock 'em-sock 'em campaign." He said his win "sent a message all over this state and around the country that Louisiana is together and that after tonight it will be united."

Johnston said he understood why working-class Louisianans who have suffered through an economic recessiohn would feel resentful toward government. "To all the people . . . who've had tough times . . . we offer the hand of goodwill," Johnston said.

Duke's political appeal is rooted in resentment -- a combination of the disillusionment that Americans of many ideologies now feel toward government and the political establishment, plus the racial resentment festering among many whites who fear that social programs such as affirmative action and welfare have given minorities an undeserved advantage in society. His campaign speeches were littered with references to affirmative action and welfare -- references that always seemed to strike a chord with audiences.

In many respects, those feelings are precisely the ones the Republican Party has successfully cultivated over the past 25 years in transforming the South into a two-party region where whites vote preponderantly for the GOP.

But while much of Duke's message is familiar, his reputation -- former Klansman, American Nazi Party sympathizer, president of the white-power National Association for the Advancement of White People, salesman of pro-Hitler books -- has been a source of great embarrassment and dismay for the state and national Republican Party.

The Republican establishment, dreading the notion of Duke as the party's standard-bearer in November, in the end worked as hard to ensure Johnston's reelection as the Democrats did, first persuading Bagert to drop out and then using the party apparatus to get out the vote in upscale white enclaves where Duke was considered yet another blight on the state's already tarnished reputation.

Louisiana voters approved a state lottery by better than 2 to 1, and in the Second Congressional District, two Democrats, state Sen. William Jefferson and Marc Morial, son of former mayor Dutch Morial, appeared headed for a runoff in their contest to succeed Rep. Corinne C. "Lindy" Boggs (D), who is retiring.