Hartford Hospital and UnitedHealth Group, the nation's largest health insurer, are in a hard-fought contract negotiation that could leave thousands of customers facing higher out-of-pocket expenses if the current agreement expires Oct. 28. "Hartford Hospital wants consumers to pay 30 percent more over the next three years for services received at their facilities," said Daryl Richard, spokesman for UnitedHealth Group. The contract affects both Hartford Hospital and its affiliate, The Hospital of Central Connecticut in New Britain and Southington.