The pandemic has forced the Food and Drug Administration to postpone hundreds of drug company inspections, creating an enormous backlog that is delaying new drug approvals and leading the industry to warn of impending shortages of existing medicines.

Pandemic-related travel restrictions and safety concerns have also hampered the F.D.A.’s ability to ensure the safety of the ever-increasing number of imported medicines, which make up more than 60 percent of the drugs sold in the United States.

“Regardless of where drugs are manufactured, domestically or overseas, the F.D.A. has the responsibility to ensure they are effective and safe,” said Mary Denigan-Macauley, the director of health care, public health and private markets for the Government Accountability Office, a congressional watchdog agency. “Any drop in inspections, or backlog, is concerning.”

The numbers show a steep decline. The F.D.A. conducted 52 inspections of domestic pharmaceutical plants from March 2020, when the pandemic took hold in the United States, to Oct. 1, compared with 400 during the same months in 2019, according to the G.A.O. Inspections of foreign manufacturing facilities have been at a virtual standstill for months.

F.D.A. officials said they sharply curtailed the inspections to protect their investigators, following guidelines from the Centers for Disease Control and Prevention, which discouraged federal employees from travel during the pandemic.

But some people in both industry and public health communities say that federal drug inspections are essential, and that the agency should bypass travel restrictions.

“I think they can and they should,” said Dr. Michael Carome, the director of Public Citizen’s Health Research Group, a nonprofit advocacy organization. “They should be considered essential workers and they should be vaccinated as soon as possible.”

In interviews, F.D.A. officials denied that the large drop in inspections had slowed drug approvals. But a number of drug companies, including Spectrum Pharmaceuticals, Biocon Biologics and Bristol Myers Squibb, have issued statements noting deferred F.D.A. action because of the agency’s inability to conduct inspections.