Mr. Taylor started his career in 1976 as an F.D.A. staff lawyer and over the next three decades migrated among government, industry and academia. He returned to the F.D.A. in 1991 as deputy commissioner for policy and moved in 1994 to head the Department of Agriculture’s meat inspection service.

Image Michael R. Taylor was named to a new position at the F.D.A. Credit... Alfan Dangin/F.D.A. Center for Veterinary Medicine

Since July, he has served as a senior adviser to Commissioner Margaret Hamburg of the F.D.A. He once worked for Monsanto, the agribusiness giant, leading some in the organic movement to oppose his appointment.

Mr. Taylor is popular among many food-safety and nutrition advocates, who call him intelligent and courageous. But he stumbled in his first major policy initiative since returning to the agency in July, and his considerable experience may have been his undoing.

Fifteen years ago, Mr. Taylor took the top job at the Food Safety and Inspection Service, the unit within the Agriculture Department that oversees meat inspections. Within weeks, he told a gathering of meat industry executives that the government would soon insist on tougher safety standards. An uproar ensued, but Mr. Taylor prevailed.

Then in November, a few months after rejoining the F.D.A., Mr. Taylor told a conclave of oyster industry officials that voluntary efforts to eliminate deaths associated with consumption of live Gulf Coast oysters harvested in warm months had not worked, and that the agency would soon ban their sale. Same speech, different audience.

But after members of Congress protested, the agency indefinitely delayed the new rules. (Mr. Taylor said that the agency was still committed to its goal of reducing oyster-related deaths.)

Dr. David Acheson, who was until last year the F.D.A.’s top food official, said the oyster reversal was the result of an alarming naïveté on Mr. Taylor’s part that seriously damaged the agency’s credibility. Dr. Acheson criticized Mr. Taylor for failing to live up to President Obama’s promise to increase significantly the safety of the nation’s food supply.