The cargo ship Limari in Baltimore, Md. (Ricky Carioti/ The Washington Post )

America’s ailing ports are almost invisible amid the country’s failing infrastructure, overshadowed by deteriorating transit systems, the flickering electrical grid, water systems that leak one-quarter of their load, and the need for new roads and bridges.

But the stuff that passes through ports is hardly invisible.

“We move stuff,” said Rick Calhoun, whose barge company moved 105 different kinds of it last year.

“You walk around Target or a Wal-Mart and you see a lot of stuff,” said Jerry A. Bridges, who runs the Virginia Port Authority, “and the consumer never thinks about how it got there, so there’s not a lot of thought about keeping the ports sustainable.”

Keeping stuff moving through the nation’s outdated ports and inland waterways, preparing to handle a new breed of ships too big for many shallow harbors, and keeping the United States competitive in a global economy where most goods are moved by water will require spending $30 billion by 2020, more than twice as much as is being spent today.

The estimate was presented Thursday in a report by the American Society of Civil Engineers, a professional trade group that has commissioned a series of reports on the gap between current spending on infrastructure and the funding needed to repair or replace systems at the end of their lifespan.

“To remain globally competitive, this is a critical time for investment,” said Andrew W. Herr­mann, president of the society.

The society’s economic analysis drew a stark portrait of the consequences if nothing is done to improve 300 commercial port facilities, to dredge deeper channels, to replace dams and locks on 12,000 miles of inland waterway, and to relieve traffic congestion around ports.

The report said that $42.2 trillion in goods passed through U.S. ports in 2010. Without massive new investments, the report estimated export losses of $270 billion by 2020 and a $697 billion drop in gross domestic product. That loss of production equates to 738,000 jobs, the report said.

The need for port investment is particularly acute on the East Coast. When a project to widen the Panama Canal is complete in 2015, new mega-ships full of Asian goods will pass through. Norfolk and Baltimore can accommodate the ships’ deep keels, but few other ports can. So, a rush is on to dig deeper channels and build port facilities that can handle the loads. New York has a unique issue: the Bayonne Bridge must be elevated to accommodate the ships that pass underneath.

Josh Kallmer, a lawyer who worked in the Office of the U.S. Trade Representative during the administration of George W. Bush, said that with 90 percent of the world’s economic growth coming outside of the United States, the ability to export goods is crucial even in an increasingly service-based world.

“They still require physical stuff that needs to move across borders,” Kallmer said. “The role for ports will, if anything, increase. Water-borne transportation is a critical part of global engagement.”

While the engineers group said it hoped that the analysis and three earlier reports on the need for infrastructure spending would become fodder for debate in this election year, Calhoun said he spent three frustrating days lobbying on Capitol Hill.

“Spend is a word that has a bad connotation in this town,” Calhoun said, “but what we’re talking about is investment. You don’t build this stuff in a day. Some locks and dams take up to 20 years.”

While he called the society’s report “invaluable” in drawing attention to the port issues, Calhoun and others acknowledged that port deterioration happens silently.

“There hasn’t been a crisis to bring to the forefront the importance of ports and waterways,” Bridges said.

Crumbling roads, bridge collapses, electrical brownouts and subway breakdowns capture public attention.

“If we don’t invest [in ports], you won’t notice it or feel it,” Calhoun said. “But it will cost American jobs and it will increase the cost of things we buy. It will all be reflected in our bottom line.”