A black businessman overwhelmed a Ku Klux Klan supporter yesterday in an Arkansas runoff for the Republican nomination for lieutenant governor.

In South Carolina, state Sen. Theo Mitchell won the Democratic gubernatorial nomination and will face popular Republican Gov. Carroll A. Campbell Jr. in the fall. Mitchell, who would become the state's first black governor if he beats Campbell, defeated white state Sen. Ernest Passailaigue in Tuesday's primary election.

Atlantic City Mayor James L. Usry, under indictment on charges of political corruption, lost a non-partisan runoff to City Councilman Jim Whelan. The vote was 62 percent for Whelan to 38 percent for Usry, who was the city's first black mayor.

In Trenton, county Freeholder Douglas Palmer scored a close victory over Mayor Carmen Armenti to apparently become the city's first black mayor. Armenti called for a recount.

In unofficial returns in Arkansas, Kenneth "Muskie" Harris, an executive with a Little Rock company, had 86 percent to 14 percent for Ralph Forbes, a former member of the American Nazi Party who advocates separate governments for blacks and whites. Harris, who finished behind Forbes in the initial primary, will be an underdog in November against the Democratic nominee, former representative Jim Guy Tucker.

"The world has learned today that the people of Arkansas {are} ready to change their image and reshape her future," Harris told supporters after his victory. "We have finally rejected the old tactics of the KKK and the neo-Nazis, and white supremacists' effort to deceive the public."

With 98 percent of South Carolina precincts reported, Mitchell, a 16-year veteran of the legislature, had 60 percent and Passailaigue, who is serving his first term, had 40 percent.

"He's going to be the next governor of South Carolina," Passailaigue said of Mitchell.

In Maine, state Attorney General James E. Tierney conceded his Democratic congressional race to state Sen. Thomas Andrews even while he was still leading in incomplete returns. With 69 percent of the precincts reported, Tierney had 36 percent to Andrews with 34 percent. Three other candidates trailed.

On the GOP side, former congressman David Emery defeated state Rep. John McCormick. With 68 percent of precincts reported, Emery led McCormick 63 to 37 percent. Emery, who changed his position on abortion, now supports abortion rights; McCormick opposes abortion.

Andrews and Emery will vie for the seat of Rep. Joseph E. Brennan (D-Maine), who is trying to regain the governorship.

North Dakota voters rejected a referendum to raise sales taxes from 5 to 6 percent for a year to improve education. With 81 percent of precincts reported, the measure failed 59 to 41 percent.

North Dakotans also turned out Labor Commissioner Byron Knutson, who had been accused of sloppy management. In a three-way race, Craig Hagen, a political newcomer who will not reach the minimum age of 25 for the office until after the primary, led with 50 percent; S.F. "Buckshot" Hoffner, head of the state Centennial Commission, had 31 percent; Knutson had 19 percent. Hagen and Hoffner will compete in November.