The National Assn. of Broadcast Employees and Technicians accused NBC on Wednesday of "union-busting" and vowed to continue its three-month strike as long as the network stands by its final offer to the union's 2,000 producers, writers and technicians. Government-mediated talks aimed at resolving the strike broke off Tuesday with no further bargaining sessions scheduled. Federal Mediation and Conciliation Service mediators met with representatives of the two sides for about six hours but "were not able to make any progress," Gayle Wineriter, special assistant to the director of the agency, said in a statement. The union's members at NBC walked off the job June 29 when the company implemented a contract that had not been approved by the union.