Community activists say the project’s supporters have ignored the negative effects it would have on the neighborhood already hurt by pollution, but those who back it contend that it is the most environmentally friendly way to grow businesses in the region and maintain the port’s dominance.

“We have to start moving things faster and cleaner, and we have to have the infrastructure to do that as close to the port as you can, which is what this does,” said Wally Baker, the chairman of Beat the Canal, a coalition of industry and labor groups supporting projects that they say will bring thousands of jobs to the area. “The last thing we want to do is create more uncertainty. That’s the kind of goofy thing that drives business away from California.”

The ports of Los Angeles and Long Beach have long been economic engines for the region, which is now home to the nation’s largest hub of distribution warehouses that sort the imported goods before they are sent to retailers across the country.

Roughly 40 percent of the country’s container imports, including cars, clothing and household items, mostly from Asia, pass through the two ports, making it the sixth-busiest harbor in the world. Many here worry that competition with ports on the East Coast is the most important threat, because so many of the products that arrive in Long Beach and Los Angeles are on their way elsewhere, often crisscrossing through a web of trains and trucks to get to consumers in the East.