Zohran Mamdani, the Democratic nominee for mayor of New York City, said on Thursday that he intended to apologize for comments he made in 2020 calling the New York Police Department “racist, anti-queer & a major threat to public safety.”

He said that the remarks, which he wrote in June 2020 in a social media post in support of the defund the police movement, were made after the police killing of George Floyd in Minneapolis a month earlier.

The comments were made “at the height of frustration,” he said in an interview with The New York Times, and were not reflective of his current campaign or “my view of public safety and the fact that police will be critical partners in delivering public safety.”

Mr. Mamdani’s post from 2020 has been recirculated by his political opponents, who have used his previous criticism of the police to portray him as weak on issues of public safety. Mr. Mamdani, a New York State assemblyman, is far ahead of his three rivals, who include Mayor Eric Adams, a former police captain who has consistently placed fourth in recent polling.

When he was asked if he should apologize to the city’s police officers, he paused noticeably before answering. He then went on to explain how his views had changed. After he was asked again if he owed officers an apology, he said, “Yes.”

Mr. Mamdani’s statements on Thursday came amid recent attempts to reach out to the police rank-and-file, an effort to address one of his biggest political vulnerabilities. His past criticism of the police has fed the skepticism and even hostility expressed by many police officers, who are wary of the changes he plans to make to the department.

But as Mr. Mamdani, a democratic socialist, began his long-shot bid to become the Democratic nominee for mayor last year, he abandoned some of his most provocative views. In recent months, he has sought to downplay others.

During the 30-minute interview Thursday, Mr. Mamdani reiterated his plan to keep the department staffed at the budgeted level of 35,000, although the number of uniformed officers stands at 33,740, according to department figures. Other candidates have said they would hire thousands more officers.

Mr. Mamdani has vowed to create a Department of Community Safety which would dispatch mental health workers, rather than the police, to respond to 911 calls from people in crisis; he contends that it would free up more police officers to tackle violent crimes like shootings and robberies.

Mr. Mamdani also said that he was bracing for President Trump to dispatch the National Guard to New York City.

“I think that it is inevitable that he will seek to deploy the National Guard in New York City,” Mr. Mamdani said. “I think it’s incumbent upon all of us to be prepared for that as opposed to treating it as simply a possibility.”

Until Thursday, Mr. Mamdani had stopped short of an apology for his 2020 remarks, saying only that his past statements were “out of step” with his current position. His vow on Thursday to apologize drew mixed responses from police union leaders.

Louis Turco, head of the lieutenants union, which endorsed Mr. Adams, called Mr. Mamdani’s comments “a good step,” noting he made them on the anniversary of the Sept. 11 terrorist attacks.

“We all make mistakes. We all get caught up,” he said. “But that’s when you grow up and you say ‘I was wrong and I apologize,’ and we move on.”

The 2020 comments were “demeaning” and “derogatory,” said Lieutenant Turco, who has stated that he would not meet with Mr. Mamdani until he had apologized.

“You want to say the policies are racist or the policies are transphobic, that’s one thing. But not the membership,” he said. “I’m pleased that he recognized that his words had a negative effect on the men and women of the N.Y.P.D. and he’s recognizing that and he wants to apologize for it.”

Scott Munro, president of the detectives’ union, was not swayed by Mr. Mamdani’s comments, which he characterized as “disgusting” and “pathetic.”

“He can apologize all he wants because this is an election year,” he said. “Right now, I don’t think he’s capable of keeping police officers safe in New York City.”

Over the summer, 13 law enforcement unions endorsed Mr. Adams, though the Police Benevolent Association, the city’s largest law enforcement union, has yet to endorse any mayoral candidate.

Patrick Hendry, president of the union, which supported President Trump during the 2020 campaign, said that Mr. Mamdani’s “words of support” were important, but needed “to be backed up with action.”

“We need elected leaders who not only support cops on the campaign trail, but who will work with us every single day to improve our safety, quality of life and compensation as we protect New York City.”

In the interview, Mr. Mamdani said he was worried that President Trump and his allies had already used the killing of Charlie Kirk on Wednesday as an excuse to go after critics and activists on the left.

“This is quite a terrifying time in our country,” Mr. Mamdani said, adding that leaders should be focusing on their “shared humanity” and not the “intensification” of a hostile atmosphere.

Since Mr. Kirk’s fatal shooting in Utah, Mr. Mamdani said, he has received new threats on his own life. He said he is frightened for his staff and the people close to him, including the security officials assigned to guard him.

During the interview, which took place at The Times, a security official stood sentry, looking out across the newsroom.

The threats “won’t change how I campaign,” Mr. Mamdani said. “It won’t change how I move through the city that I love.”