SAN FRANCISCO/TOKYO (Reuters) – A labor dispute at ports on the U.S. West Coast is disrupting supply chains across the Pacific, forcing some Asian suppliers to resort to costly air freight and pushing up shipping rates as more freighters are caught up in long queues to dock. With ports near gridlock and cargo delays being felt throughout the U.S. economy, President Barack Obama on Saturday dispatched Labor Secretary Tom Perez to California to try to broker an agreement on a new contract between dockworkers and the group representing shippers and terminal operators.