Because the federal government contributes to the salaries of many members of the Navajo Nation, Mr. Begaye said the lack of pay would hurt families on the reservation, where a single salary can support a family of six, 10 or even 12 people. Mr. Begaye said loan sharks have started circling, leaving fliers on cars and doorsteps.

“It just kind of snowballs into our people doing things that they know they shouldn’t do and further financially obligating themselves,” Mr. Begaye said. “They have to keep their heater going. They have to keep their water on.”

On the Bois Forte Indian Reservation in northern Minnesota, tribal officials have instituted a hiring freeze and are planning to meet later this week to discuss budget cuts. Cathy Chavers, the tribe’s chairwoman, said tribal functions were continuing for now, but “it will probably come down to minimal, minimal basic services” if the shutdown lasts another month.

Already, police officers on her reservation, who are employees of the federal government and not the tribe, were being forced to work without pay.

“These officers are putting their lives on the line,” Ms. Chavers said, “and they don’t know if they’re going to get a paycheck or not.”

Tribes are making plans for how much longer they can operate, while not knowing whether they will be reimbursed for shutdown-related expenses. Officials with the Oneida Nation of Wisconsin said that they had made contingency plans but that they could manage at least another month without any cuts. The Shoshone-Bannock Tribes in Idaho posted on Facebook that they had enough money to operate at full strength through Saturday, but would then have to re-evaluate.