LOS ANGELES, May 9 (Reuters) - Three supermarket chains and the unions representing Southern California grocery workers said on Wednesday they would return to the bargaining table, a day after workers' unions walked out of ongoing contract talks, raising the fear of an acrimonious strike.

Local unions representing the 65,000 Southern California grocery employees of Kroger Co.'s <KR.N> Ralphs, Supervalu Inc.'s <SVU.N> Albertsons and Safeway Inc.'s <SWY.N> Vons and Pavilions said they broke off talks on Tuesday after the grocers made "unacceptable demands" on health benefits and wages.

But Wednesday afternoon, a spokesman for the United Food and Commercial Workers unions, Mike Shimpock, told Reuters their side was "going to try and get negotiations back on track. I don't know what that means right now."

The grocery chains issued a statement repeating their commitment to meet next week for talks. Before the unions walked out, May 14 had been set as a date for the next meeting.

Neither side invoked a 72-hour cancellation rule, which triggers the expiration of the contract if both sides cannot come to agreement within three days.

It was the second time in the negotiations, which began in March, that the local unions had walked away. Overseen by a federal mediator, the talks center on wages and health coverage for workers who saw benefits reduced after a debilitating five- month labor dispute that devastated the industry in 2003-2004.

UNION POWER DEBATED

Ken Jacobs, chair of the University of California Berkeley Center for Labor Research and Education, said talks may drag out for some time.

"Given the drastic erosion of union members' health benefits under the last contract, I think the union is in a position where it's going to, or needs to, hold firm in improving health benefits," he said.

Labor disputes and competition from nonunion rivals such as Wal-Mart Stores Inc. <WMT.N> that are expanding their food offerings have troubled some industry analysts.

"The issues holding up the talks are somewhat intractable," wrote Bank of America analyst Scott Mushkin in a research report published before the resumption of talks was announced.

In the report, he wrote that a strike was a "real possibility with obvious negative implications for the stocks."

Labor expert Jacobs said factors boosting the unions' power include a recently-signed contract with rivals Stater Bros. and Gelson's, owned by Arden Group Inc.<ARDNA.O>; the fact the Wal-Mart threat has not been as severe as first expected; and that newly-hired workers who receive less than veteran employees under the existing contract will push for improved benefits.

But some question whether the union has the strength to rally labor around the prospect of another strike, a suggestion Shimpock dispelled.

One long-time Ralph's employee, who declined to be named for fear of repercussions, said the local unions had lost the support of the bulk of members who remember the last strike and are unwilling to endure a second. Were a strike to be called, many workers would quit and find jobs elsewhere rather than picket, he said.

"People are disappointed. I can speak for everyone here, no one wants a strike," said the worker, who has been employed at the chain for 13 years and was an active advocate for the union during the previous labor dispute.

"I have a feeling the union is not budging ... I hate to say it -- the union is a bit greedy. They know they're losing power."