At a time when the general economy is slowing, medical-care costs are rising at a virtually unprecedented rate. This dynamic is leading the Reagan administration to design new cost-control mechanisms for Medicare and Medicaid that would sharply limit reimbursement levels for providers and increase the cost of care for consumers. This phenomenon is also calling into serious question the effectiveness of the four-year-old "Voluntary Effort to Contain Health Care Costs," which the nation's major private health interests launched in their successful effort to thwart former President Carter's hospital-cost-control legislation.Although the Reagan administration is firmly on record as being in . . .