WASHINGTON — Kathleen Sebelius, the secretary of health and human services, said Wednesday that the government needed to fix hundreds of problems with the website for the federal health insurance marketplace, but she categorically rejected bipartisan calls to delay parts of the new health care law.

She made her comments at a hearing of the Senate Finance Committee hours after the Obama administration disclosed that the chief information officer at the Centers for Medicare and Medicaid Services would retire. His office supervised the creation of the troubled website.

The official, Tony Trenkle, will step down on Nov. 15 “to take a position in the private sector,” according to an email circulated among agency employees. He has supervised the spending of $2 billion a year on information technology products and services, including the development of the website.

Mr. Trenkle, reached by telephone on Wednesday, declined to discuss his plans. “I can’t speak with you,” he said.