WASHINGTON — Civil rights groups called on President-elect Donald J. Trump on Monday to publicly condemn extremist movements that are espousing racism in his name after hundreds of white nationalist sympathizers spent the weekend in Washington debating ways to preserve white culture.

Mr. Trump has been accused of fanning the flames of hate groups with his hard-line positions on immigration, his hesitance to denounce the former Klansman David Duke and his occasional promotion of white nationalist accounts on Twitter. While Mr. Trump has called for an end to hate crimes and said he wants to bring the country together, he has not been full throated on expressing disapproval of the alt-right, a rebranded white nationalist movement.

“We would like him to stand up and denounce these folks,” Heidi Beirich, who tracks hate groups for the Southern Poverty Law Center, said of Mr. Trump. “It’s inexplicable. The longer it goes on, the more you have to wonder if it’s not intentional.”

The conference, held at a federal building named after Ronald Reagan, drew about 275 attendees from around the country and attracted droves of “anti-fascist” protesters. Speakers preached the virtues of a white “ethno-state,” railed against Jews and lauded Mr. Trump’s election as a victory with Nazi salutes.