Communications networks battered by the Atlantic superstorm Sandy continued to improve, even as power failures and sputtering backup generators hampered gains in New York City and other hard-hit areas.

The proportion of mobile-phone sites that were still out of service has dropped to 19 percent, down from 25 percent two days earlier, according to the U.S. Federal Communications Commission. Verizon Communications Inc., the largest phone company in the region, said thousands of employees have fanned out across New York and New Jersey to repair damage, though power outages and blocked roads slowed efforts.

“The availability of fuel to keep generators delivering backup power to switching facilities and other critical network equipment is an increasing challenge,” New York-based Verizon said yesterday in a statement. “Verizon is working with federal, state and local government officials to obtain the fuel crucial to maintaining communications and Internet access.”

Sandy, the largest tropical system ever measured in the Atlantic, struck Oct. 29. It killed at least 75 people in the U.S., flooded subway tunnels and knocked out power to as many as 8.5 million homes and businesses along the East Coast, including about half of New Jersey. The storm will cost telephone and cable companies as much as $600 million in repair and cleanup costs, according to James Ratcliffe, a New York-based analyst with Barclays Plc.

Flooded Headquarters

Engineers and technicians with Verizon restored backup power to four critical facilities in lower Manhattan and one on Long Island that incurred severe flood damage and lost commercial power, Bill Kula, a spokesman, said in an e-mail. The locations included the company’s own headquarters at 140 West Street, which became a symbol of Sandy’s wrath after Verizon posted a picture of its flooded lobby on the Web.

Verizon has the most exposure to the damage because it has many customers in the Northeast with land-line service, Ratcliffe said in a note. Cablevision Systems Corp., meanwhile, has the biggest portion of its customer base without service. The cable company, which focuses on the New York market, said yesterday that about 1.5 million subscribers can’t connect to its service because their power is out.

“Restoration efforts in the hardest hit areas -- including New York and New Jersey -- continue to be more difficult,” David Turetsky, chief of the FCC’s Public Safety & Homeland Security Bureau, said in a statement. Finding enough fuel for generator-powered equipment is a major concern, he said.

No Power

Cablevision, based in Bethpage, New York, has about 3.3 million video subscribers in total. The company said yesterday that the number of customers without power, and therefore without service, had dropped by about 100,000.

Across the wider storm-stricken area, cable outages declined to about 12 percent to 14 percent, from an initial rate of about 25 percent, Turetsky said. The agency assessed 158 counties across 10 states and the District of Columbia.

AT&T Inc. was working with New York officials to deploy generator-driven charging stations in the city, Michael Balmoris, a spokesman, said in an e-mail. AT&T and Verizon, the two largest U.S. wireless carriers, invited people to charge their mobile devices at their stores.

Sprint Nextel Corp. also was struggling with power failures in New York and New Jersey, Crystal Davis, a spokeswoman for the third-largest carrier, said in an e-mail. In New York City, about three-fourths of the network was working, Davis said.

Sprint’s networks were fully restored in seven states and the District of Columbia, she said. More than 90 percent were operational in four more states, and 80 percent were restored in New York, New Jersey and Connecticut.

T-Mobile USA Inc.’s network was “close to normal” outside of lower Manhattan, the fourth-largest U.S wireless carrier said in a statement.