CHARLOTTE, N.C.-A hospital, clinic and insurer are developing a new HMO to serve the Charlotte and Mecklenburg County markets. The joint venture partners are Presbyterian Hospital and Nalle Clinic, both in Charlotte, and Blue Cross and Blue Shield of North Carolina, based in Durham. The partners say the HMO, which has yet to be named, is expected to begin enrollment later this year. The 579-bed hospital and 100-physician clinic have been affiliated since last June, when they formed a joint venture to pursue managed-care contracts (July 11, 1994, p. 34). The clinic's physicians also are members of the hospital's physician-hospital organization, Presbyterian Health Services.