Louisiana's U.S. Senate race has become a head-to-head match between an incumbent Democrat reluctantly supported by Republican party leaders over a Republican who was once a member of the Ku Klux Klan.

State Sen. Ben Bagert dropped out of the primary race Thursday, saying he feared his Republican candidacy could force incumbent Democrat J. Bennett Johnston into a runoff with ex-Klansman and Republican state Rep. David Duke. Under Louisiana's open primary system, all candidates run on one ballot, regardless of party affiliation. A runoff between the top two finishers is held if no one receives a majority of votes.Bagert said his polls indicated he might pull just enough votes to keep Johnston from getting more than 50 percent of the vote and force the three-term incumbent into a runoff with Duke.

GOP leaders say such an event would embarrass the state and the Republican party nationally. Eight Republican senators endorsed Johnston earlier this week.

"All my supporters understand how important this race is," Bagert said in announcing his withdrawal. "The state's on trial. The state has a chance to show what it is, what its values are, to the rest of the country.

"I'm not endorsing anybody, but I'm not voting for David Duke," he said. Asked if he would vote for Johnston, he said, "Yes, reluctantly."

A poll released Wednesday by Mason-Dixon Opinion Research of Columbia, Md., showed Johnston was the choice of 53 percent of voters surveyed. Duke drew 26 percent, while Bagert polled 8 percent, with 13 percent undecided. The poll of 825 registered voters had a margin of error of 3.5 percent.

Duke scoffed at the idea that Bagert's conservative Republican support might move to Johnston's camp.

"They sure don't want a liberal senator to go back there and vote for more taxes and for affirmative action," he said in a television interview.

Johnston has often voted a moderate-to-conservative line in Washington, supporting defense spending and aid to the Nicaraguan contras.

But Duke and Bagert have accused him of being too liberal for Louisiana, citing his role in helping defeat former President Reagan's nomination of Judge Robert Bork to the Supreme Court and his support for the Civil Rights Act of 1990.

Meanwhile, Duke has said his days as a Klansman and neo-Nazi are behind him, but critics say they don't believe him. They point to his selling of Nazi literature from his suburban New Orleans office, a practice he stopped in 1989 after Republican leaders reported it to the media.

Duke ran for president in 1988, first as a Democrat, later as a populist. He ran for the state Legislature as a Republican in 1989 and narrowly defeated another Republican in an all-white suburban New Orleans district.