WASHINGTON — A year after the race-fueled violence in Charlottesville, Va., hundreds of demonstrators gathered in a narrow park there on Sunday to denounce racism and hate groups, hours before white nationalists planned to rally in front of the White House.
By noon, organizers and participants from last August’s counterdemonstrations in Charlottesville had massed in Booker T. Washington Park, just north of the University of Virginia, and a mile from the area downtown where a 32-year-old woman was killed by a white supremacist.
Dozens of State Police officers formed a barricade that blocked protesters from moving outside a checkpoint. With no sign of white supremacists there, tensions were confined to interactions between the left-leaning protesters and law enforcement.
Later on Sunday, white nationalists planned to gather in Lafayette Square just north of the White House to mark the anniversary of their Charlottesville rally, with thousands of counterprotesters poised to oppose their message.
While the city braced for the possibility of violence, the usual Sunday calm prevailed in downtown Washington in the morning and afternoon. Groups of about a half-dozen police officers in neon yellow vests were stationed at street corners, and police signs posted on lampposts declared that the possession of firearms was prohibited for the day.
At Lafayette Square, where the white nationalists and counterdemonstrators planned to rally, a maze of barricades had been erected to manage the two sides once they arrived in the evening. Stacks of placards calling for an end to white supremacy lay on the grass. And a handful of counterdemonstrators, including some Black Lives Matter activists, gave interviews to television cameras on the sidewalk.
By midmorning, law enforcement officers had cleared out the park. And by early afternoon, hundreds of counterprotesters had assembled in Freedom Plaza, just east of the White House. In suburban Virginia, police officers in helmets entered a subway stop where white nationalists had begun to gather to make their way into Washington.
On Saturday, President Trump issued a general call for unity, denouncing “all types of racism,” but not specifically condemning white supremacism.
“Riots in Charlottesville a year ago resulted in senseless death and division,” he wrote on Twitter on Saturday morning. “We must come together as a nation. I condemn all types of racism and acts of violence. Peace to ALL Americans!”
Mr. Trump’s words were reminiscent of his reluctance a year ago after the deadly Charlottesville rally to single out white nationalists, instead blaming “both sides” for the violence, and appearing to draw a moral equivalence between hate groups and counterprotests.
The rally on Sunday, called Unite the Right II, is scheduled to take over Lafayette Square for two hours in the evening. The Unite the Right group plans to have up to 400 people at the rally, according to the permit it received from the National Park Service, though the number in attendance could be considerably smaller.
An antiracism group, the Answer Coalition, was granted a permit in Lafayette Square for a group more than three times the size of Unite the Right’s. At least two groups of counterprotesters have permits to gather at the Lincoln Memorial.
On Sunday afternoon, white nationalists are scheduled to march from Foggy Bottom, a neighborhood just west of the White House, to the small quadrant of Lafayette Square they are designated to occupy.
A counterprotest group is scheduled to march to the same place from the opposite direction, starting at Freedom Plaza.
Once the formal program begins, Jason Kessler, who helped organize last year’s Charlottesville rally, is scheduled to speak to the crowd, as is David Duke, the former politician and Ku Klux Klan leader.
The Park Service, which permits around 750 First Amendment demonstrations annually in the national capital region, granted one last week to Mr. Kessler. “In anyone’s recollection, there has never been a First Amendment permit that’s been denied,” said Mike Litterst, a Park Service spokesman. “There wasn’t much discussion or question of whether or not it would be issued.”
Last year in Charlottesville, neo-Nazis, Ku Klux Klansmen and other members of hate groups marched through the University of Virginia campus shouting anti-Semitic slogans, then fought with counterprotesters in the city streets. A man who espoused neo-Nazi views is accused of driving his vehicle into the counterdemonstators, killing a 32-year-old woman, Heather D. Heyer.
The chance of that kind of spontaneous mayhem has led to weeks of planning between Washington’s law enforcement agencies, which have developed proposals to guard marches leading to the rally and the rally itself, as well as deal with any confrontations that precede or follow it in the streets of Washington.
Sgt. James Dingeldein of the Park Police said his agency, the Washington police and the Park Service had met with Mr. Kessler and leaders of counterprotest groups to explain to them what is permissible on the grounds of the park. The Park Service has issued a detailed set of limits and prohibitions on items that can be brought in, banning some of the items that were wielded in Charlottesville. The Washington police have vowed to keep the groups separated.
“If there is potential for violence, it will be dealt with quickly,” Sergeant Dingeldein said.
Federal officials have expressed concern that violence could spill into other parts of Washington. Sergeant Dingeldein said the police agencies had riot control teams ready.
James Murray, an assistant director in the Secret Service’s Office of Protective Operations, warned in a letter on Monday to the Park Service that it was possible that tension between groups could lead to the same kind of violence that occurred in Portland, Ore., last weekend, where a right-wing rally turned violent after, the police said, a group began throwing rocks and bottles at officers.
Mr. Murray wrote that some of the same counterprotesters who seized downtown streets at the presidential inauguration in January 2017 were also interested in Sunday’s demonstrations, and were “known to have engaged in violent and destructive activity.” Members of the sometimes violent movement known as antifa are expected to be among the counterprotesters on Sunday.
Muriel E. Bowser, the Washington mayor, activated the city’s emergency operations center on Thursday. At a news conference that day, she said Unite the Right participants were an anomaly among visitors to Washington.
“Very few of our visitors share the views that will be expressed in Lafayette Square this weekend,” she said.
Hawes Spencer contributed reporting from Charlottesville, Va.