Merv Griffin is giving himself an option to back away from a deal to purchase Resorts International Inc., lawyers and casino officials said. Griffin said he allowed a deadline to complete the acquisition to expire on Friday, and that any party to the proposed deal was now free to terminate its obligations. Griffin had offered to pay $36 a share for Resorts, which owns a casino and huge land holdings in Atlantic City, N.J., as well as land and a casino in the Bahamas. Griffin would take the company private by buying out developer Donald J. Trump’s controlling stock and all remaining shares. Griffin’s latest move could be an indication that he believes he can buy Resorts at a lower price by threatening to withdraw from the deal.