The rest were either enrolled automatically by the government, or they will receive benefits through their private health care plans. Medicare opened enrollment in the program on Nov. 15; it ends May 15.
Health and Human Services Secretary Mike Leavitt told reporters that the government expects to sign up between 28 and 30 million people for the benefit during its first year. Medicare provides health care to 42 million older and disabled Americans.
"We're encouraged by the early results," Leavitt said. "You'll find you'll save money and you'll never have to worry about high drug costs in the future."
The government's figures are as of Dec. 13. Another 500,000 people are expected to enroll in January, officials said.
Critics have complained about a confusing array of choices for seniors signing up for the program. The programs are managed by private insurance companies that contract with the federal government; the government pays some of the drug costs. Additional subsidies are available for low-income people.
The federal government estimates that it will spend about $724 billion over 10 years to provide the benefit.