Gov. Ricardo A. Rosselló told reporters that over the next two days, more than half a million barrels of diesel fuel and nearly a million barrels of gasoline would reach Puerto Rico. The fuel is badly needed to power emergency generators and to distribute food and other supplies across the island.

Mr. Rosselló said that the Defense Department had increased its footprint on Puerto Rico to 6,400 people, from roughly 4,600 two days earlier, with more coming, and that other federal agencies were also sending more staff to aid in the island’s recovery from Hurricane Maria, which smashed through the island on Sept. 20.