Milwaukee is facing a deepening lead crisis in its schools, and it suddenly finds itself without help from the country’s top public health agency.

Four children in the Milwaukee Public Schools have been found to be exposed to high levels of lead in the last six months. Investigators have discovered seven schools with flaking lead paint and lead dust inside classrooms and basements. Three school buildings have been shuttered so far, and officials said that more are expected to follow — as soon as next week — as the investigation expands.

In the past, school districts have turned to the Centers for Disease Control and Prevention to help manage lead problems. But weeks ago, the commissioner of the Milwaukee health department was told that a toxicologist and epidemiologist from the C.D.C., both lead experts who were expected to assist city officials with the local response, had been fired from the agency.

Then the Milwaukee health department was dealt an even sharper blow: Its request for federal assistance from C.D.C. experts to help manage the lead crisis, known as an Epi-Aid, had been formally denied.

“There is no bat phone anymore,” Dr. Michael Totoraitis, the Milwaukee health commissioner, said in an interview. “I can’t pick up and call my colleagues at the C.D.C. about lead poisoning anymore.”

The C.D.C. is already reeling from layoffs targeting 2,400 employees, nearly one-fifth of its work force. The Department of Health and Human Services, which oversees the C.D.C., did not respond to a request for comment. The Trump administration has said that it is cutting positions throughout the federal government to reduce spending and bureaucratic bloat.