LOS ANGELES — The union representing thousands of West Coast dockworkers yesterday reached a tentative contract deal with shippers that promises to keep ports running and avoid another blow to the U.S. economy.

The International Longshore and Warehouse Union announced the six-year agreement following months of negotiations with the Pacific Maritime Association. Neither side released details of the deal, which still must be ratified by union and PMA members.

The contract covers more than 25,000 dockworkers at 29 West Coast ports.

The current six-year contract covering dockworkers expired July 1 without a strike or lockout, with both sides insisting they wanted to keep the ports running smoothly — even if they had to keep talking after the deadline.

The decision was a welcome break for the teetering U.S. economy, since the billions of dollars in cargo handled by the 29 ports represents about 11 percent of the U.S. gross domestic product.