The Obama administration's timeline for having ready the new health care law's online sign-up system "was just flat out wrong," outgoing Health and Human Services Secretary Kathleen Sebelius said in an interview that aired Sunday.
The departing health chief also said the two months when the federal healthcare.gov website was plagued with technical problems were "a pretty dismal time" and the low point of her five-year tenure. But she defended the law's impact and said millions of Americans now have access to health care because of it.
"People have competitive choices and real information for the first time ever in this insurance market," said Sebelius, who last week announced her resignation.
Republicans demanded that Sebelius resign last October after the flawed launch of the health care reform law which is Obama's signature domestic policy achievement. They have tried to make "Obamacare" the key issue in November's national election when control of Congress will be at stake.
Sebelius acknowledged the rocky rollout for the online sign-up system fraught with technical problems that left Americans frustrated.
"Clearly, the estimate that it was ready to go Oct. 1 was just flat out wrong," Sebelius said.
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HealthCare.gov was envisioned as the principal place for people to buy insurance from private companies — made more affordable by government subsidies —under Obama's health care law. But its first few weeks were an embarrassment for the administration and its allies, resulting in a drop in the polls for Democrats and a revival of Republican prospects in the 2014 election even though the party was blamed for last year's unpopular partial government shutdown.
"Well, I think there's no question — and I've said this many times — that the launch of the website was terribly flawed and terribly difficult," Sebelius said.
Obama set a Dec. 1 deadline to have the website repaired, a move that left Sebelius nervous, she said.
Read MoreObamacare enrollment tally to surpass 7.5 million: US official
"Having failed once at the front of October, the first of December became a critical juncture," she said. "That was a pretty scary date."
Sebelius' resignation comes just a week after sign-ups for insurance coverage on federal and state exchanges ended, enrolling 7.1 million people and exceeding initial expectations. Enrollment has since increased to 7.5 million as people were given extra time to complete applications.
The departing secretary said she decided after the 2012 presidential election that she wanted to leave the administration but decided to stay through the initial sign-up period for the new health care program. Sebelius said Obama did not try to convince her to stay through the end of his term.
"I thought it was fair to either commit till January of 2017 or leave with enough time that he would get a strong, competent leader," Sebelius said.
Obama has nominated White House budget director Sylvia Mathews Burwell to replace Sebelius.
Sebelius spoke to NBC television's "Meet the Press."