Moving to fill a key vacancy as his administration swings to the enormous task of implementing the new health care law, President Barack Obama has reportedly settled on a choice to lead the Centers for Medicare & Medicaid Services.

The New York Times reported Saturday that President Barack Obama will name Dr. Donald Berwick to the position, which has been without a permanent chief since Mark McClellan stepped down in October 2006.

The vacancy was increasingly a source of anxiety for Democrats — and a target for Republicans — as the health care legislation moved toward passage. The new law expands Medicaid and calls for substantial savings out of Medicare.

Berwick is a pediatrician and president of the Institute for Healthcare Improvement in Cambridge, Mass. The nomination requires Senate confirmation.