The controversial manager of the Bush administration's federal family planning initiatives resigned abruptly today to focus on a mysterious "action" being taken against the medical practice he ran before taking the job just four months ago.

Dr. Eric Keroack has been a lightning rod for criticism since his nomination last fall to run the Office of Population Affairs, an agency that manages federal reproductive health programs. From the very start, Keroack drew fire from critics of his opposition to birth control and support for abstinence education.

Today, Keroack e-mailed staff at the Department of Health and Human Services to explain his surprise decision.

"The Massachusetts Office of Medicaid has undertaken an action against my private medical practice in Massachusetts," he wrote.

Just what was that action remains a mystery. The e-mail did not elaborate and state officials could not be reached for comment. HHS officials said privacy laws forbid them from sharing more details. Members of Congress had not been informed of the action.

Keroack is an obstetrician and gynecologist who, according to his official biography, "served in private practice in Massachusetts for nearly 20 years" before joining the administration. From 2000 to 2005, he also served as medical director for A Woman's Concern, a network of Christian "pregnancy health services" clinics throughout Massachusetts that aim to talk women out of considering abortion.

In November, 14 Democratic senators sent a letter to HHS Secretary Mike Leavitt urging him to withdraw Keroack's appointment.

"This appointment is another example of the administration allowing ideology to trump science," the senators wrote. "And it could jeopardize vital services on which large numbers of women and families depend."

In his e-mail, Keroack expressed confidence he would be cleared of whatever scrutiny he has been placed under by the state.

"I immediately engaged legal counsel to initiate an appeals process," he wrote. "My attorney feels confident that misunderstandings have occurred and that upon further review of the facts during the appeals process, this action will be reversed. However, the appeals process will present a significant distraction to my ability to remain focused on my duties."

His departure is effective immediately. In a brief statement released late today, Dr. John Agwunobi, assistant secretary for health, said he accepted Keroack's resignation as deputy assistant secretary of the Office of Population Affairs Wednesday.

"The department will move forward as expeditiously as possible to fill this position," Agwunobi wrote.