Mayor Brandon Johnson of Chicago defended his record and his city’s policy of not proactively helping immigration officials during hours of hostile questioning from congressional Republicans on Wednesday.

Mr. Johnson, a Democrat who is almost two years into his term, repeatedly insisted that Chicago’s practice of not cooperating with immigration agents, unless those agents have criminal arrest warrants, did not violate federal law. Those policies, he argued, made the city safer and allowed residents to help the police solve crimes without fear of deportation.

“Violent crime in the city of Chicago is down,” the mayor said. “It continues to go down under my leadership.”

Republicans were not having it. They argued that Chicago was breaking federal laws and making the country more dangerous by failing to assist Immigration and Customs Enforcement agents in arresting and deporting undocumented immigrants.

“You’re putting the interests of illegal immigrants above the interest of taxpayers in Chicago,” Representative Darin LaHood, an Illinois Republican whose district does not include Chicago, said to Mr. Johnson.

A longstanding city ordinance in Chicago bars local officials from asking about a person’s immigration status, proactively sharing it with federal officials in most cases or allowing immigration agents to enter certain city facilities without a warrant.

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