WASHINGTON - Republican Party leaders are sharpening their attacks on David Duke as the former Ku Klux Klan leader prepares a conservative challenge to President Bush in several of next year's GOP primaries.

Duke, who lost the Louisiana governor's race two weeks ago, had been scheduled to announce his political plans today but yesterday postponed his announcement until Wednesday. An aide said Duke needed more time to gather information on ballot-access rules.

As Duke's plans to enter GOP primaries became known over the weekend, national GOP leaders fired fresh salvos in his direction.

"David Duke is a Nazi Klansman who, in his own background, is despicable and should be shunned in American politics," House Republican Whip Newt Gingrich of Georgia said yesterday on NBC-TV's "Meet the Press."

Republican National Committee Chairman Clayton Yeutter called Duke a "full-time con man" and predicted he would garner little support in primaries. "He's a repulsive political figure in my judgment, and the American public will not be conned by anyone of that nature," Yeutter said.

Still, Yeutter predicted Bush would name a campaign team in the next two weeks, earlier than originally planned.

The daily attacks by Democrats on Bush are the main reason for the stepped-up political schedule, but the planned challenges by Duke and conservative commentator Patrick Buchanan also have disrupted the administration's re-election strategy.

"I think he's going to have these two guys biting at his heels," Gingrich said. He predicted Buchanan could get as much as 45 percent of the vote in the New Hampshire presidential primary.

Neither Buchanan nor Duke is seen as a real threat to Bush's nomination. But for a White House trying to rebound from recent political missteps as Bush's poll standings fall, the challenges have to be taken seriously.

Buchanan is scheduled to announce his plans Dec. 10, less than a week after Duke.