WASHINGTON — The No. 2 official at the Centers for Medicare and Medicaid Services, who supervised the troubled rollout of President Obama's health care law, is retiring, administration officials said Monday.

The official, Michelle Snyder, is the agency's chief operating officer, in charge of day-to-day activities and the allocation of resources, including budget and personnel.

Technology experts who built the website for the federal insurance exchange, HealthCare.gov, reported to her.

Ms. Snyder is the second administration official to depart since problems with the website frustrated millions of people trying to buy insurance and caused acute political embarrassment to Mr. Obama.

The chief information officer at the Medicare agency, Tony Trenkle, stepped down in November to take a job in the private sector.

Marilyn B. Tavenner, the administrator of the Medicare agency, said Ms. Snyder was retiring this week "after 41 years of outstanding public service."

"While we celebrate her distinguished career, we are also sadly saying farewell to a good friend and a key member of the agency's leadership team," Ms. Tavenner said in an email to agency employees. "Michelle's intelligence, experience and formidable work ethic have been indispensable to me and to many of you during her tenure."

Agency officials said that Ms. Snyder's deputy, Tim Love, would fill her position on an acting basis.

Asked about Ms. Snyder's plans, an agency official said Monday, "It's her personal decision to retire now."

Ms. Tavenner said that Ms. Snyder was prepared to step down at the end of 2012, but stayed on the job "at my request to help me with the challenges facing C.M.S. in 2013."

Her official biography says that Ms. Snyder was responsible for "standing up new programs and activities required by the Affordable Care Act."

The agency provides health insurance to more than 100 million people and spends more than $800 billion a year, which is substantially more than the Defense Department budget.

A former agency official who had predicted Ms. Snyder's departure said Monday: "She had to go. She was responsible for the implementation of Obamacare. She controlled all the resources to get it done. She was in charge of information technology. She controlled personnel and budget."

At a congressional hearing on Oct. 30, Kathleen Sebelius, the secretary of health and human services, was asked who was responsible for developing the federal website, and she named Ms. Snyder.

But Ms. Sebelius quickly added: "Michelle Snyder is not responsible for those debacles. Hold me accountable for the debacle. I'm responsible."

Many of the initial problems have been fixed, but their effects linger, as the agency and insurers try to correct enrollment records.