“Clearly, there have been problems with rolling out the test,” said Dr. Thomas Frieden, former director of the C.D.C. “There are a lot of frustrated doctors and patients and health departments.”

Still, Dr. Frieden said he thought the situation was improving. Other experts, although supportive of the agency, were mystified that federal officials could have committed so many missteps.

“The incompetence has really exceeded what anyone would expect with the C.D.C.,” said Dr. Michael Mina, an epidemiologist at Harvard University. “This is not a difficult problem to solve in the world of viruses.”

Despite repeated inquiries from The New York Times, C.D.C. officials have never provided a full account of the obstacles the agency faced in producing a diagnostic test. On Monday, officials appeared to have removed figures on the agency website counting how many Americans had been tested, and abruptly canceled a news conference just as it was to begin.