Reports that the Trump administration might swiftly carry out an immigration crackdown, perhaps as early as this week, have left some neighborhoods reeling in cities like Chicago.

While the timing and locations of targeted arrests are uncertain, and though Tom Homan, Mr. Trump’s border czar, said as recently as Saturday that “no decision has been made yet,” the prospect of raids has consumed the conversation in Chicago neighborhoods such as Pilsen and Little Village, city leaders said.

“People are terrified,” said the Rev. Emma Lozano, a leader at Lincoln Methodist Church in Pilsen whose congregation includes many Latin American families. She said she moved her services online in recent weeks because wary parishioners were trying to keep low profiles. Some children have been reluctant to go to school, fearing they could come home to find that their parents had been taken into custody, she said.

Ms. Lozano, who has spent decades ministering to migrants, and at times has sheltered undocumented immigrants in the church, said the situation had never felt as tenuous. “The threat has always been there,” Ms. Lozano said, but “this feels massive.”

Around Chicago, one of the cities that has been mentioned as a possible location for the Trump administration’s ramping up of efforts to deport undocumented immigrants, activists have been holding meetings to advise people about their legal rights should immigration agents come knocking. Families have been drafting powers of attorney to make issues like custody and property ownership easier to handle.

The Illinois Coalition for Immigrant and Refugee Rights, a nonprofit, has issued guidance on its website to any Illinois residents concerned about deportation, advising them not to open the door for immigration officers, not to discuss their immigration status with any law enforcement officials and not to sign anything that they do not understand. Families should provide their children’s school with an emergency contact in case parents are detained, the group said.

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