But federal officials said that the fastest-growing type of Medicare Advantage plan generally does not coordinate care, does not save money for Medicare and has been at the center of marketing abuses.

These “private fee-for-service plans” allow patients to go to any doctor or hospital that will provide care on terms set by the insurer. In most cases, no one manages the care. And some patients have found that they have less access to care, because their doctors refuse to take patients in private fee-for-service plans.

Moreover, those plans may be more expensive than traditional Medicare for some patients, because the co-payments for some services may be higher. The Medicare Payment Advisory Commission says that the cost to the government is also higher because it pays the private fee-for-service plans, on average, 19 percent more than the cost of traditional Medicare.

Richard S. Foster, chief actuary for the Medicare program, said “the additional payments to Medicare Advantage plans, above and beyond the costs” of traditional Medicare, were causing higher premiums for all beneficiaries and speeding the depletion of the Hospital Insurance Trust Fund for Medicare.

Almost one-fifth of the 43 million Medicare beneficiaries are now in some type of private plan.

Much of the growth in private fee-for-service plans has come in rural areas, where doctors and hospitals are often in short supply.