Updated

The federal government started annual Medicare enrollment Thursday, amid a percolating fight on Capitol Hill over an expected increase in the insurance program's Part B premiums.

Monthly premiums will stay flat, on average, for prescription drug plans and are falling on average for private plans offered through Medicare Advantage, a popular alternative to traditional Medicare. The average prescription drug premium will be $32.50, while the average Medicare Advantage premium will fall to $32.91.

"Health needs can change in a year, so it is important for people with Medicare to use this time to check to see if they are getting the best price and best quality plan available," said Andy Slavitt, acting administrator for the Centers for Medicare and Medicaid Services.

But Medicare Part B, the part of Medicare that covers outpatient care such as doctor's visits, is projected to become much more expensive for about one-third of enrollees. Those premiums are projected to rise by about 52 percent next year for the top third of highest-income enrollees, unless Congress agrees on a solution by the end of the year.

The increase is triggered by an index tied to Social Security benefits, which won't undergo a cost-of-living increase this year. That means the federal government is prohibited from raising Medicare premiums for certain, lower-income seniors, forcing the government to concentrate the price hikes on those with more financial assets.

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