Mark McClellan, who oversaw the federal government's health insurance programs for the poor and elderly, is joining the think tank world.

McClellan will focus on developing ways to improve health care and eliminate excess costs. He will serve as a visiting senior fellow at a center for regulatory studies run by two think tanks — The Brookings Institution and the American Enterprise Institute.

An economist and physician, McClellan helped implement the Medicare prescription drug benefit. As administrator of the Centers for Medicare and Medicaid Services, his agency paid for about $1 out of every $4 spent on health care in the United States. He announced his resignation this fall.

McClellan will identify steps to speed the development of new treatments and on reforming payment and regulatory systems, a press release from the two organizations said Monday.