Talk of potential mergers in the medical insurance industry has doctors and hospitals worried about health plans having too much clout over consumer choices and prices. There has been speculation that some of the nation's biggest health plans may be looking to consolidate, including a possible takeover of Humana Inc. by Aetna Inc., as well as UnitedHealth Group's interest in Coventry Health Care Inc. Providers worry that increased consolidation would add to their concerns about deteriorating reimbursement from government health programs as the federal deficit rises and state budgets tighten.