WASHINGTON — Federal health officials warned impatient governors on Friday against relaxing pandemic control measures, saying that a recent steep drop in coronavirus cases and deaths in the United States may be leveling off at a very high number — a shift that the director of the Centers for Disease Control and Prevention said “must be taken extremely seriously.”

Across the United States, and the world, the coronavirus seems to be loosening its stranglehold. The deadly curve of cases, hospitalizations and deaths has yo-yoed before, but never has it plunged so steeply and so fast.

Is this it, then? Is this the beginning of the end? After a year of being pummeled by grim statistics and scolded for wanting human contact, many Americans feel a long-promised deliverance is at hand.