“This thing” is the $21 million plug-in station that Mayor Michael R. Bloomberg and the Port Authority of New York and New Jersey agreed to introduce in Red Hook several years ago in an effort to eliminate 1,200 tons of carbon dioxide, 25 tons of nitrous oxide and tons of hazardous particulate matter spewed out each year by cruise ships idling off Brooklyn’s coast.

When not using shore power, a single cruise ship docked for one day can emit as much diesel exhaust as 34,400 idling tractor-trailers, according to an independent analysis verified by the Environmental Protection Agency. When a ship is plugged in, the agency said, its exhaust is nearly eliminated.

But the system has hardly been used after going into operation in 2016. And New York City is expected to announce design plans next year that would expand and modernize terminals in Brooklyn and Manhattan to accommodate the world’s largest cruise ships, and more of them.

Yet there is no plan to further expand the shore power system.

Neighborhood residents, led by Mr. Armstrong, are sounding the alarm. They want the pollution controls that were promised by the Bloomberg administration. They fault the city and state for failing to force the matter, and the cruise line companies for failing to use the system.

Carnival Cruise, which owns the three big ships that dock regularly in Brooklyn, including the Queen Mary 2, agrees that the issue is important.

“Protecting the environment and environmental compliance are top priorities,” Carnival’s spokesman, Roger Frizzell, said in an email. Forty percent of Carnival’s fleet is equipped to use shore power, he added.

“We have invested millions of dollars to equip our ships with shore power capabilities and other emerging next-generation technologies that are a pathway to lower emissions and a cleaner environment,” he wrote.