A contract dispute between Blue Cross and the Care New England hospital group has raised worries about whether Blue Cross subscribers will be able get care at Rhode Island-based Butler, Women & Infants and Kent hospitals after Dec. 31. But the chief executives of both companies say they expect to resolve their differences. Negotiators are meeting regularly and still have three months before the current contract expires. Care New England recently drew attention to the problem by sending letters to doctors and employees, telling them that after Dec. 31, Care New England might be dropped from the provider network of Blue Cross & Blue Shield of Rhode Island.