LOS ANGELES (AP)-- Doors will be closed Thanksgiving Day at nearly 860 Southern California supermarkets because of the labor dispute between three supermarket operators and some 70,000 striking or locked-out grocery clerks.

The chains' stores — Albertsons, Vons, Pavilions and Ralphs — traditionally have opened for business for at least a few hours on Thanksgiving Day. They decided last week, however, not to open during the holiday. The stores reopened Friday. "It was a business decision," Albertsons Inc. spokeswoman Stacia Levenfeld said Wednesday.

Calls to Kroger Co., which owns Ralphs, and Safeway Inc., which operates the Vons and Pavilion stores, were not immediately returned Wednesday.

"They do keep saying that they're operating business as usual and the strike is not affecting them at all, but this is a clear admission that the staff that they've hired can't handle it," said Ellen Anreder, spokeswoman for the United Food and Commercial Workers union.

Grocery workers' picket lines have dissuaded many would-be customers from shopping at Vons, Pavilions and Albertsons stores for nearly seven weeks. Ralphs stores have seen business pick up since Oct. 31, when the union called off picket lines at the chain and ordered the workers to picket stores run by the other supermarket operators.

Growing frustration with the long-running labor dispute and the need to shop for Thanksgiving feasts drove many people in recent days to cross the picket lines, although some customers reported shortages after doing so.

The union turned up the pressure on the chains Monday by extending its picket lines to the chains' distribution centers. Teamster truck drivers and warehouse employees refused to cross the lines, forcing the chains to hire more replacement workers to keep supplies flowing.

At least one union local did not trust that the chains would close their doors Thursday, and planned to keep workers manning picket lines at 39 stores. "Our picketers don't want to surrender our lines," said Connie Leyva, president of UFCW Local 1428 in Claremont. "Our Albertsons lines will be up and running and our Vons lines will be up with a skeleton crew, two people at a time." The labor dispute centers over the cost of health insurance coverage for employees. It has affected stores from San Luis Obispo to San Diego

CAPTION Striking California grocery clerks vowed to expand their picket lines into Northern California, the District of Columbia and Maryland even as Teamsters came to their defense with plans to choke off food supplies to targeted stores during Thanksgiving.