WASHINGTON (AP) - Port operators along the East Coast have reached a tentative deal on a new contract with the union for longshoremen, averting a possible strike that would have crippled operations at 15 ports, according to a federal mediator. The deal was announced late Friday in a statement from George Cohen, head of the Federal Mediation and Conciliation Service. Cohen, who has been leading the talks since last year, says the agreement remains subject to ratification by both parties and additional local union negotiations. But he says local talks would continue without threat of interrupting any port operation. Cohen declined to offer any details on the deal. Both sides had been in intense negotiations since the previous contract ended in September. The parties initially postponed the deadline to reach a deal for 90 days, then postponed it again until Dec. 31. Just before the end of last year, the parties resolved a thorny issue involving royalty payments made to union members for each container unloaded. They extended the deadline on the rest of the issues until Feb. 6. Major ports that would have been frozen in a strike included the Port Authority of New York and New Jersey; Savannah, Ga.; Houston; and Hampton Roads, Va. Other ports that would have been affected include Boston; Delaware River; Baltimore; Wilmington, N.C.; Charleston, S.C.; Jacksonville, Fla.; Port Everglades, Fla.; Miami; Tampa, Fla.; Mobile, Ala.; and New Orleans.