H.M.O.'s Return For a Piece Of Medicare Pie
Managed care companies that pulled out of areas across country few years ago are returning now that federal Medicare reimbursement rates have gone up; Bush administration's plan caled for $46 billion to be pumped into these health insurance programs over next 10 years; number of Medicare beneficiaries enrolling in managed care plans has started to rise in Hernando County, Fla; Humana Inc's chief executive Michael McCallister comments; map; chart (M)
