WASHINGTON — Ever since a pro-Trump mob attacked the Capitol on Jan. 6, Republicans have been trying to shift the national conversation away from that dark, violent day and onto what they say are the problems of the Biden administration: a troubled pullout from Afghanistan, an overtaxed southern border and rising inflation.

Then, a former campaign operative of President Donald J. Trump announced that he was organizing hundreds of protesters to return to the Capitol on Saturday for a rally in support of the defendants charged in connection with the deadly assault, which left dozens of officers bloodied.

Bad memories of the violence rushed back. The Capitol Police announced that they were reinstalling a security fence around the complex and were aware of “concerning online chatter” from extremist groups. And many Republican lawmakers, gritting their teeth, said they wanted nothing to do with the event. Not a single member of Congress has confirmed his or her attendance, even those who have been most outspoken in portraying the rioters as patriots who have been persecuted for their political beliefs.

“There are a lot of clearly angry people who want to march on the Capitol,” said Senator John Thune of South Dakota, the No. 2 Republican. “I haven’t talked to a single Republican up here in the Senate that has encouraged or enabled anything like that.”

Nevertheless, the “Justice for J6” rally, to be held at noon on Saturday at the foot of Capitol Hill, has created a predicament for Republicans, who are caught between a hard-right base including many voters who consider the rioters righteous and a desire to distance themselves from the attack and its political fallout.

“Anytime the attention is on Joe Biden it’s good for Republicans, and anytime the attention is on Jan. 6 it’s bad for Republicans,” said John Feehery, a Republican strategist and veteran of Capitol Hill. “The only hope Democrats have of keeping the House is to make Jan. 6 the issue of the campaign. They know that, and we know that. The only people who don’t seem to know that are the activists.”

That has left top Republicans in an uncomfortable spot, toiling to distance themselves from an event that is certain to dredge up the subject of the Capitol riot — and that could potentially spiral out of control — but wary of offending voters who sympathize with the cause.

Representative Kevin McCarthy, Republican of California and the minority leader, told reporters this week that he did not expect any lawmaker in his party to attend, but his office had no response to questions about whether he supported the rally or was dissuading people from attending. Representatives Steve Scalise of Louisiana and Elise Stefanik of New York, the second- and third-ranking House Republicans, have been similarly taciturn about the event.

Even Representative Marjorie Taylor Greene, a Georgia Republican who has been among the most vocal critics of the treatment of the Jan. 6 suspects, said she would not be attending the rally, even as she defended the inspiration behind it.

“There’s a two-track justice system in America, and the treatment of the J6 political prisoners compared with violent antifa/BLM rioters proves it,” she said in a lengthy email statement.

Ms. Greene said she condemned the violence that occurred during the riot, but said she believed that “illegal aliens are treated better than many of the J6 accused.”

In shunning the event, Republicans are following the lead of Mr. Trump himself, who has been uncharacteristically silent about it even though he has in the past defended the mob.

Mr. Trump, aides said, has little interest in engaging with the protest and has no plans to be anywhere near Washington on Saturday. Instead, his schedule includes a golf tournament at his Bedminster, N.J., club before he heads back down to his Mar-a-Lago resort in Florida, according to people familiar with his schedule.

Mr. Trump views the planned protest as a setup that the news media will use against him regardless of the outcome, according to people familiar with his thinking.

But disquiet in the party is real on behalf of the Jan. 6 defendants, particularly those who are charged with nonviolent offenses, Mr. Feehery said. He said many Republican voters believed that the Trump supporters who stormed the Capitol would have received lighter treatment if they had been supporting a left-wing cause.

“I can appreciate why Republicans don’t want anything to do with this,” he said, “but there is a lot of angst in the Republican base.”

Capitol Police officials have urged anyone considering violence to stay home instead of attending Saturday’s rally, which was organized by Matt Braynard, a former Trump campaign operative, and his organization, Look Ahead America.

Mr. Braynard has pledged that his group will be peaceful, unlike the mob that stormed the Capitol on Jan. 6, when about 140 police officers were injured and several people died.

Mr. Braynard has argued that the brutal attacks on police officers during the assault were the work of a “few bad apples” and accused the Biden administration of targeting the “peaceful Trump supporters who entered the Capitol with selective prosecutions based on their political beliefs.”

“These people’s faces are up on billboards,” he said. “They’re losing their jobs. They’re losing their homes. They’re spending all their savings on attorneys. They’re going bankrupt for doing what on any other day, for any other cause would have gotten you a $50 fine and a slap on the wrist.”

Those kinds of appeals had found support among the right flank of the Republican Party in the House — including Ms. Greene and Representatives Matt Gaetz of Florida, Louie Gohmert of Texas, Bob Good of Virginia, and Paul Gosar and Andy Biggs of Arizona. In July, those members held a news conference on behalf of the Jan. 6 defendants, but as of Wednesday, none of them had confirmed their attendance to Saturday’s rally.

Mr. Braynard has had difficulty securing high-profile speakers for his event. To date, he has announced the attendance of two congressional hopefuls, including Joe Kent, a primary challenger to Representative Jaime Herrera Beutler of Washington, who was one of 10 Republicans to vote to impeach Mr. Trump over his role in the attack.

Mr. Braynard also announced that Ralph Norman, Republican of South Carolina, would attend a future “Justice for J6” rally in Columbia, S.C. But Mr. Norman’s spokesman said he would not be attending.

Asked if he believed Republican leaders were discouraging his efforts, Mr. Braynard said, “You’d have to ask them that.”

In the Senate, Republicans have also worked to distance themselves from the rally, with many arguing that it is a distraction.

Senator Mitch McConnell of Kentucky, the minority leader, said he believed the police were “well equipped to handle” whatever might occur.

Senator Josh Hawley, a Missouri Republican who led objections to President Biden’s victory on Jan. 6, said he was not attending and was focusing on other issues. Senator Tommy Tuberville of Alabama, another Republican who objected to the election results and was in close contact with Mr. Trump’s inner circle before and during the riot, also said he would not participate.

“I don’t expect a lot of people there,” Mr. Tuberville said. “I haven’t heard anything about it. I will not be there.”

Still others said they had little sympathy for the Jan. 6 defendants, and encouraged a forceful response from the police should Saturday’s crowd turn violent.

“They need to take a firm line, buddy,” said Senator Lindsey Graham of South Carolina, an on-again, off-again ally of Mr. Trump’s. “If anybody gets out of line, they need to whack ’em.”

Annie Karni contributed reporting.