AUGUSTA — Top leadership changes are in store for MaineGeneral Health, hospital officials said Wednesday.

Beginning Jan. 1, 2013, Chuck Hays will become CEO of MaineGeneral Health, the parent organization of MaineGeneral Medical Center, where he now is CEO.

In his new role, he will oversee a system that has a $480 million annual operating budget and 4,000 employees.

MaineGeneral Health is the third-largest health care system in the state and in the midst of building a regional hospital that will consolidate inpatient services now provided in Augusta and Waterville.

Scott Bullock, currently president and CEO of MaineGeneral Health, will remain as president and support Hays in policy, planning, physician recruitment, government relations and fundraising areas, according to a news release from the hospital.

The announcement of the change came from Robert Marden, board chairman of MaineGeneral Health.

“It’s result of many years of them working together with Scott mentoring Chuck and Chuck rising to the occasion,” Marden said. “It’s rare this can come about so naturally and seamlessly.”

Bullock, 60, of Waterville, has been CEO of MaineGeneral Health since 1999 and CEO of hospitals and health systems for 29 years.

“I’ve reached a point where I want to have less stress and be more supportive to Chuck, who will be an excellent CEO,” Bullock said Wednesday. “I just want to be no longer responsible for such a large organization. It’s a very complex and demanding job.”

Bullock has led the hospital system through a number of expansions and changes, the largest of which is the hospital under construction in north Augusta.

Bullock said he began talking to the board a year ago about scaling back his responsibilities.

“I had brought MaineGeneral to the point I had been determined to do, and I felt at that point Chuck was more than capable,” Bullock said.

The board conducted its own evaluation of Hays before selecting him.

Early in Bullock’s tenure with MaineGeneral, the organization had 2,700 employees and annual operating revenue of about $166 million.

He said the organization continues to evolve to keep pace with the needs of the population, advances in technology and best practices.

Hays, 48, of Manchester, joined MaineGeneral Health in 1997 as a vice president.

As CEO of MaineGeneral Medical Center, he oversees the hospitals in Augusta and Waterville, the Harold Alfond Center for Cancer Care in Augusta, and physicians’ practices, including the new Musculoskeletal Center in Augusta.

In January he will pick up responsibility for the system’s long-term care facilities, Granite Hill Estates, and HealthReach HomeCare & Hospice.

He said he also will work with the board on strategic planning, “although Scott’s done a marvelous job setting us up for the future, with the new regional hospital opening in 16 months.”