The three major grocers in Los Angeles said they have struck an agreement that includes a provision to lock out all employees from all stores if a strike is called at any one of the chains. Supervalu Inc.’s Albertsons, Kroger Co.’s Ralphs and Safeway Inc.’s Vons units said the deal also will provide financial assistance to any of the companies if they are struck by workers represented by the United Food and Commercial Workers union. The grocers said the decision was made in response to the strike threat. Last month, workers at Albertsons gave the union authority to strike if contract negotiations broke down. The current contract was due to expire in March and was extended until April 9.