WASHINGTON  The basic Medicare premium will shoot up next year by 15 percent, to $110.50 a month, federal officials said Monday.

The increase means that monthly premiums would top $100 for the first time, a stark indication of the rise in medical costs that is driving the debate in Congress about a broad overhaul of the health care system.

About 12 million people, or 27 percent of Medicare beneficiaries, will have to pay higher premiums or have the additional amounts paid on their behalf. The other 73 percent will be shielded from the increase because, under federal law, their Medicare premiums cannot go up more than the increase in their Social Security benefits, and Social Security officials announced last week that there would be no increase in benefits in 2010 because inflation had been extremely low.

Kathleen Sebelius, the secretary of health and human services, urged the Senate to approve a bill, already passed by the House, to block the scheduled increase in Medicare premiums.