By Noel Randewich

SAN FRANCISCO (Reuters) - Growing numbers of freighters were backed up around the two busiest U.S. cargo hubs on Sunday because of a dispute between shipping companies and dockworkers that has led to a partial shutdown of ports along the West Coast.

With cargo delays rippling through the U.S. economy, Japanese carmaker Honda Motor Co Ltd said it planned to slow production at some of its North American plants starting on Monday because of a lack of parts from Asia.

Under pressure to address the months-long strife, President Barack Obama on Saturday dispatched U.S. Labor Secretary Tom Perez to California to help broker an agreement.

By Sunday morning, 34 container ships, tankers and other cargo vessels were waiting to dock at the ports of Los Angeles and Long Beach, California, up from 32 on Saturday, said Lee Peterson, a spokesman for the port of Long Beach.

Cargo ships waiting at anchor and unable to load their goods were visible from highways and beaches for miles along the coast, an unusual spectacle, he said.

Those delays have slowed deliveries of a wide range of goods, from agricultural produce to housewares and apparel, leading retailers to pressure Obama to intervene.

Honda, which had already resorted to transporting some parts by airplane, said it would adjust production at plants making models including the Civic, CR-V, Accord and Acura.

"This is a fluid situation due to the uncertainty of the situation at the West Coast ports," spokesman Mark Morrison told Reuters by email. "At this time, we do not have a sufficient supply of several critical parts to keep the production lines running smoothly and efficiently."

The Obama administration's move to send Perez came after shippers vowed to prevent the loading and unloading of freight through Monday from container ships at the 29 ports, barring a settlement in talks with the dock workers' union.

The shipping companies said they were unwilling to pay union workers higher wages for weekend shifts and the Presidents' Day holiday on Monday while productivity declined and cargo backups reached the point of near gridlock, after months of chronic congestion in freight traffic.

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The Department of Labor is working on Perez's schedule, spokeswoman Xochitl Hinojosa said on Sunday.

“The secretary will meet with the parties to urge them to resolve their dispute quickly at the bargaining table," she said.

On Friday, negotiators for the union representing 20,000 dockworkers at the ports and management's bargaining agent, the Pacific Maritime Association, agreed to a federal mediator's request for a 48-hour news blackout. The two sides held a bargaining session on Thursday that marked their first face-to-face meeting in nearly a week.

(Additional reporting by Jeff Mason in Rancho Mirage, Calif.; Editing by Stephen Powell, Nick Zieminski and Peter Cooney)