Once the Corps of Engineers departs, the Puerto Rico Electric Power Authority, known as Prepa, will be tasked with completing unfinished repairs to the power grid. At a hearing last week of the Senate Committee on Energy and Natural Resources in Washington, lawmakers sounded skeptical that Prepa, which has come under fierce scrutiny over its early response to the storm, is up to the job. Representative González-Colón has asked FEMA to extend the Corps’ stay.

“We sure want to know that you really are ready,” Senator Lisa Murkowski of Alaska told Prepa’s new chief, Walter Higgins, at the hearing.

“We feel that we are ready,” Mr. Higgins said. But, he added, “I don’t doubt that we will have some growing pains.”

In Las Piedras, which sits on the hills south of El Yunque National Forest, people who have electricity say it goes out often. “If a little bit of wind blows through, we will lose power,” said Roberto Rosado, 53, who still has metal shutters on his sliding doors. “We just lost power now. This is an everyday occurrence.”

Mayor Miguel López, who is known as Micky, recently blocked two of the three power crews from leaving his town. “There was no other option,” said Mr. López, whose unorthodox strategy succeeded in keeping the linemen at work.

His director of emergency management, Xavier Muñoz, said the one upside of Maria was that it had scared residents into taking hurricane plans seriously.

“Shelters are going to get full,” he predicted. “I have 220 cots right now, and I think that’s not going to be enough.”