Whoever President-elect Obama names to lead the massive agency that manages Medicare and Medicaid will have to tackle major issues from day one, several of the agency’s former chiefs agreed.

The incoming Obama administration plans significant changes in the way Medicare, Medicaid and the State Children’s Health Insurance Program (SCHIP) are run, and the president-elect’s choice for administrator of the Centers for Medicare and Medicaid Services (CMS) will be the one tasked with putting those new policies in place.

All the while, the new Medicare chief will be responsible for the day-to-day operations of an agency with 4,400 employees, a $676 billion annual budget and a duty to provide healthcare to 44.6 million people enrolled in Medicare, 51 million in Medicaid and 6.3 million in SCHIP.

“That’s going to be an extremely, extremely important position,” said Tommy Thompson, who was HHS secretary during President Bush’s first term and now is a partner at Akin, Gump, Strauss, Hauer & Feld.

“The wonderful and terrifying thing about running CMS is that you never know what’s lurking around the corner,” said Nancy-Ann DeParle, who ran the agency during President Clinton’s second term, when it was known as the Healthcare Financing Administration. “There’s just so many things that can go wrong,” said DeParle, an investment adviser at J.P. Morgan.

“The challenges of running that place are unbelievable in a slow time. It’s just a huge place,” said Tom Scully, who was Bush’s first CMS administrator. Scully is a senior counsel at Alton & Bird and a general partner at the investment firm Welsh, Carson, Anderson & Stowe.

Obama and Daschle will look for a candidate who has experience managing a large organization, knowledge of the healthcare system and good political relationships, the former officials agreed.

“It’s a terrific job because it marries policy and operations in a way almost no other position does,” said Gail Wilensky, who ran the agency during the George H.W. Bush administration and now is a senior fellow at Project HOPE.

Speculation has centered on a handful of Obama insiders, Clinton White House veterans and longtime Democratic healthcare experts.

Among the names thought to be under consideration are: Obama transition team member and Center for American Progress senior fellow Jeanne Lambrew; Avalere Health President Dan Mendelson; Urban Institute scholar Robert Berenson; Georgetown University Professor and failed congressional candidate Judy Feder; and Emory University Professor Ken Thorpe.