WASHINGTON - President Joe Biden will host a meeting on Wednesday to hail progress in addressing supply chain problems weighing on the economy and threatening the holiday season, while he challenges business and union leaders to do more to ease shipping backlogs.

The Port of Los Angeles is going to 24/7 operations as a step toward helping ease the shipping snarl there and at the Port of Long Beach, a senior administration official told reporters ahead of the meeting.

In addition, the three largest carriers of goods - Wal-Mart, FedEx and UPS - plan to move toward round-the-clock operations to help speed the shipment of goods across the country, the official said.

Samsung, Home Depot and Target are also increasing their work in off-peak hours to accelerate the movement of goods, the official said.

"By taking these steps, they're saying to the rest of the supply chain, you need to move too," the official said. "Let's step it up."

White House officials, scrambling to relieve global supply bottlenecks choking U.S. ports, highways and railways, are warning that Americans may face higher prices and some empty shelves this Christmas season. They are urging patience. 

The supply crisis is driven in part by the global COVID-19 pandemic. It not only threatens to dampen U.S. spending at a critical time, it also poses a political risk for Biden.

The latest Reuters/Ipsos poll shows the economy continues to be the most important issue for Democrats and Republicans alike.

Biden will meet at 1:45 p.m. (1745 GMT) at the White House with executives from the two ports as well as from the International Longshore and Warehouse Union, the Teamsters, the AFL-CIO, Wal-Mart, FedEx, UPS, Target, the National Retail Federation, the American Trucking Association, the Pacific Maritime Association, and more.

He will speak on these efforts at 2:20 p.m. (1820 GMT).

The White House has been trying to tackle inflation-inducing supply bottlenecks of everything from meat to semiconductors, and formed a task force in June that meets weekly and named a "bottleneck" czar, John Porcari, to push private-sector companies to find ways to get goods flowing.

Thousands of shipping containers are on cargo ships offshore waiting to be offloaded at the ports of Los Angeles and Long Beach. Similar backlogs exist at ports in New York and Savannah, Georgia. A shortage of warehouse workers and truck drivers to pick up goods is partly to blame.

(Reporting By Steve Holland; Editing by Tim Ahmann and Richard Pullin) ((Steve.a.holland@thomsonreuters.com; www.twitter.com/steveholland1; 202 898 8300; Reuters Messaging: steve.holland.reuters.com@reuters.net))