In a speech in Texas, the former president also urged supporters to hold protests if prosecutors in Atlanta and New York pursued criminal charges against him.

Donald J. Trump said on Saturday that if re-elected president, he would consider pardoning those charged in the Jan. 6 attack on the United States Capitol.

He also called on his supporters in Atlanta and New York to stage large protests if prosecutors in those cities, who are investigating him and his businesses, took action against him.

Mr. Trump’s promise to consider pardons is the most he has said in support of the Jan. 6 defendants.  “If I run and I win, we will treat those people from Jan. 6 fairly,” he said, addressing a crowd at a fairground in Conroe, outside Houston, that appeared to number in the tens of thousands. “We will treat them fairly,” he repeated. “And if it requires pardons, we will give them pardons, because they are being treated so unfairly.”

At least 700 people have been arrested in connection with the Jan. 6 riot, with 11 facing seditious conspiracy charges. Some have claimed that they thought they were doing Mr. Trump’s bidding.

Mr. Trump, as president, pardoned a number of his supporters and former aides, including Michael T. Flynn, his first national security adviser, who pleaded guilty twice to lying to the FBI, and Stephen K. Bannon, his former campaign strategist and White House adviser, who was charged with defrauding donors to a privately funded effort to build a wall along the Mexican border.

Mr. Trump issued a statement late Sunday criticizing a bipartisan effort to rewrite the Electoral Count Act of 1887, a century-old law that the former president and his allies misinterpreted in their failed attempt to persuade his vice president, Mike Pence, to overturn legitimate election results. The effort to change the law is intended to prevent future similar attempts by clarifying that the vice president does not have the authority to overturn results.

Mr. Trump made the statement for the first time, describing his goal as overturning an election. However, Mr. Trump’s statement included his usual false claims about election fraud, implying that he does not believe the election was legitimate.

The statement marks an increase in the former president’s push to litigate the 2020 election, and it comes just days after Senate Minority Leader Mitch McConnell issued a public warning to Republican candidates to “respect the results of our democratic process” during an interview.

Members of both parties rebuked Mr. Trump’s pardon remarks on Sunday, including lawmakers who fled the rioters as they broke into the Capitol and Senate chamber. Max Rose, a Democrat seeking to reclaim his seat in New York from Representative Nicole Malliotakis, one of the Republicans who voted to overturn the election results, called on his opponent to condemn the remarks.

Senator Susan Collins of Maine, one of seven Republicans who voted to convict Mr. Trump in his second impeachment trial for incitement of an insurgency, said on ABC’s “This Week” on Sunday that the former president should not have made the comments, adding, “We should let the judicial process proceed.”

Senator Lindsey Graham of South Carolina, a Republican who has resurfaced as a supporter of the former president after condemning him in the aftermath of the Jan. 6 riot, called the remarks “inappropriate.”

Mr. Trump also took aim at the New York State attorney general and the Manhattan district attorney, both of whom have been investigating his businesses for possible fraud, as well as the district attorney in Fulton County, Ga., who has appointed a special grand jury to look into Mr. Trump’s efforts to overturn the state’s 2020 election results.

He urged his supporters to stage large protests in New York, Atlanta, and Washington if the investigations resulted in action against him.