WASHINGTON —  Thomas Scully (search), the Bush administration official deeply involved in drafting the Medicare bill, said Wednesday he will resign once President Bush signs the Medicare (search) overhaul into law.

Scully said he probably will take a job at one of five law or investment firms that want him to advise clients affected by the sweeping Medicare legislation.

White House officials said President Bush will sign the bill Monday, giving seniors a prescription drug benefit beginning in 2006 and private insurers a new larger role to play in health care for 40 million older and disabled Americans.

Scully said he will step down on Dec. 15 as administrator of the federal Centers for Medicare and Medicaid Services (search). The agency, a branch of the Health and Human Services Department, oversees the health insurance programs for the elderly, disabled and poor.

"I'm thrilled I stuck around to see it through. It's done," Scully said in an interview.

Scully, 46, who has run the Medicare and Medicaid programs for nearly three years, has often expressed a desire to spend more time with his three young children and earn more money.

Congressional Democratic critics of the legislation, including Sen. Edward M. Kennedy of Massachusetts, declined to comment on the matter.

But several other bill opponents said Scully's talks with potential employers during consideration of the legislation reinforced a perception that the administration favors insurers and drug companies over seniors.

"Seniors have a right to know why a White House bill that forks over billions to the HMOs and drug industries was written by a person who was apparently pursuing employment with those same industries," said David Sirota, spokesman for the Center for American Progress (search), which is run by former Clinton administration officials and aides to congressional Democrats.

Scully acknowledged that the firms have been courting him for months, through the drafting and drawn-out negotiations over the bill. But he said he received clearance from the top HHS ethics official to continue his work on the legislation.

"The fact is, I played this absolutely by the book," Scully said.

Scully said his intention to leave the administration once the Medicare bill was finished "was the worst-kept secret."

He said none of the firms that contacted him asked for any special consideration in the bill. "They all called me. I said, 'Sorry, you have to wait,"' Scully said.

Scully served in senior positions at the Office of Management and Budget (search) during the first Bush administration. Later, he served as president of the Federation of American Hospitals, the trade group representing the for-profit hospital industry.