Elon Musk said on Tuesday that he would “reverse the permanent ban” of former President Donald J. Trump on Twitter and let him back on the social network, in one of the first specific comments by the world’s richest man of how he would change the social media service.Mr. Musk, who struck a deal last month to buy Twitter for $44 billion, said at a Financial Times conference that the company’s decision to bar Mr. Trump last year for tweets about the riots at the U.S. Capitol was “a mistake because it alienated a large part of the country and did not ultimately result in Donald Trump not having a voice.” He added that it was “morally wrong and flat-out stupid” and that “permanent bans just fundamentally undermine trust in Twitter.”Mr. Musk’s remarks were a preview of the kinds of sweeping changes he might make at Twitter, which he is expected to take ownership of in the next six months. The billionaire, who also leads the electric carmaker Tesla and the rocket company SpaceX, has long supported free speech and has said that he was unhappy with how Twitter decided what could and could not be posted online.But up until Tuesday, Mr. Musk, 50, had spoken mostly in general terms and had not singled out Twitter accounts that might be affected by his takeover. He had called free speech “the bedrock of a functioning democracy” and had spoken of his desire to give people more control over their own social media feeds. But by specifying that Mr. Trump could return to the platform, Mr. Musk uncorked a political firestorm.Mr. Trump wielded Twitter for many years as both a megaphone and a cudgel, rallying his millions of followers on issues such as immigration and going after opponents. That avenue was cut off in January 2021 when Twitter, along with Facebook and other platforms, barred Mr. Trump from posting in the wake of the attack on the U.S. Capitol building. Twitter said at the time that Mr. Trump had violated policies and risked inciting violence among his supporters. Facebook banned Mr. Trump for similar reasons.Mr. Trump, who has since begun a social media platform called Truth Social, did not immediately respond to request for comment. Last month, Mr. Trump had said that even with Mr. Musk buying Twitter, he did not plan to return to the platform and was “going to stay on Truth.”A spokesman for Twitter did not immediately have a comment.Derrick Johnson, the president of the NAACP, said that free speech online needed to come with guardrails.“Mr. Musk: Free speech is wonderful, hate speech is unacceptable,” he said. “Do not allow 45 to return to the platform. Do not allow Twitter to become a petri dish for hate speech, or falsehoods that subvert our democracy.”But Jack Dorsey, a founder and board member of Twitter, said on Twitter on Tuesday that permanent bans of individual users “are a failure” of the company and largely “don’t work.” Mr. Dorsey, who had been chief executive of Twitter when Mr. Trump was barred, had said last year that booting the former president was the right decision for the company.This is a developing story. Check back for updates.