In Los Angeles, especially at moments like this, there are few jobs as critical as fire chief. And it was Ralph M. Terrazas, whom Mr. Garcetti promoted to fire chief soon after he became mayor, who appeared most at his side, offering technical updates on fire conditions and reports on how he was dispatching his 3,200-member force across this 500-square-mile city, where the speed of a response can determine whether a fire is a passing brusher or a conflagration that forces the evacuation of thousands of homes.

At the height of the disaster, 900 members of the Los Angeles Fire Department were spread out across the region, fighting three major fires and battling back scores of other outbursts. They were among an army of 2,000 firefighters, many of whom had come in from across the state to assist in the effort. Six-hundred members of the city’s police department were also assigned to the fires.

Raphael J. Sonenshein, executive director of the Pat Brown Institute for Public Affairs at California State University, Los Angeles, said that this episode had spotlighted, at least for now, the strong relationship Mr. Garcetti had with his police commissioner and the fire commissioner. Those relations have frequently been strained with mayors in the past, and that has caused problems when the city had to come together.

“When the relationship between mayor and chief is toxic — think Bradley-Gates — it’s not good of either of them when disaster strikes,” Mr. Sonenshein said, referring to Tom Bradley, who was mayor of Los Angeles from 1973 to 1993, and Daryl Gates, his police chief.

By the time Mr. Garcetti arrived on Thursday morning for a private briefing by fire and police officials at the command center for the Skirball Fire, the blaze — which at one point loomed as a potentially major threat to some of Los Angeles’ most affluent neighborhoods — was considered to be far less of a threat. But danger still loomed.

The command post at the West Los Angeles Veterans Affairs campus, just off the 405 freeway, was bustling with firefighters and police officers. Mr. Garcetti, wearing a blue City Hall windbreaker emblazoned with his name, mingled with firefighters in front of the command post, comparing photographs of the fire on their phones and trading information on what they had heard in the field.

Mr. Garcetti walked over to a map of the fire taped onto the wall as an assistant chief, Corey Rose, brought him up-to-date. The mayor dutifully scribbled notes, asking questions that reflected the decidedly technocratic spirit he has brought to City Hall. (Example: “What is the containment in Rye, do you know?” the mayor asked, inquiring about a fire in Santa Clarita.)