Park Place Entertainment Corp., Aztar Corp. and Harrah's Entertainment Inc.---three major casino firms in Las Vegas---reached tentative contract agreements with the Culinary Workers Union yesterday. The settlements come one week after the 48,000 members of the Hotel Employees and Restaurant Employees affiliated CWU voted overwhelmingly to give their elected leadership the power to call a strike if new contracts were not negotiated before their existing contracts expired on May 31. Although several major employers on Vegas? main strip have not yet reached settlements with the CWU, the likelihood of a major strike that could disrupt Vegas? recent economic recovery has been greatly reduced.