WASHINGTON — A top Obama administration official who helped oversee the rollout of HealthCare.gov will retire on Tuesday, according to an announcement from the Centers for Medicare and Medicaid Services.

The departure of CMS Chief Operating Officer Michelle Snyder comes after the agency has significantly improved performance of the online health exchange, but continues to address concerns about the site’s security.

Snyder is the second administration official to leave the agency since the system launched in October with numerous glitches that prevented users from enrolling. Tony Trenkle, who was the agency’s chief information officer, left for the private sector in November.

CMS Administrator Marilyn Tavenner announced Snyder’s retirement in an email to agency employees, saying, “Michelle’s intelligence, experience and formidable work ethic have been indispensable to me and to many of you during her tenure.”

Snyder, the highest-ranking official responsible for HealthCare.gov to exit the administration since the site’s rollout, has worked in public service for 41 years, including a stint as deputy chief operating officer for CMS. She helped the agency expand its community-based health-center programs, establish an employee mentorship program and achieve its first clean financial audit, the CMS announcement said.

A Washington Post report in November revealed that CMS staffers were aware as late as January that progress on HealthCare.gov was lagging and that adequate testing of the system might not be possible in time for the site’s start.

An inspector general’s report in August warned that CMS might not be able to fully assess the site’s security risks before the planned rollout on Oct. 1. Eleven days before that deadline, CMS Chief Information Security Officer Teresa Fryer recommended denying authorization for the HealthCare.gov launch, describing the system as a “high risk,” according to closed-door testimony she gave to House Oversight and Government Reform Committee investigators.

On Sept. 27, Snyder authorized the site to operate, with plans to regularly test for problems over the next six months. The online exchange went live five days later with myriad failures, including crashes and problems that blocked users from registering.

Rep. Darrell Issa, R-Calif., who chairs the House oversight committee, criticized Snyder in a statement on Monday for “bypassing the recommendation of CMS’ top security expert.” He attributed her actions to a “cult-like commitment officials had to the arbitrary goal of launching on October 1.”

CMS defended its security testing with its own statement on Monday, saying independent analyses showed the site to be compliant with the Federal Information Security Management Act and guidelines prescribed by the National Institutes of Standards and Technology. The agency also said last week that “there have been no successful attacks on HealthCare.gov”and that no person or group has maliciously accessed users’ personal information.

Despite early problems with HealthCare.gov, the site is functioning better amid ongoing fixes. The Obama administration said this week that more than 1.1 million Americans have signed up for insurance plans through the online portal. The Department of Health and Human Services had projected that 3.3 million people would have enrolled through the exchange by now, according to a September memo from the agency.