WASHINGTON — Signaling a shift in tone in acknowledging problems with the launch of the Affordable Care Act website, the government posted a blog Sunday taking responsibility for issues millions of Americans have had trying to sign up for health insurance.

“Unfortunately, the experience on HealthCare.gov has been frustrating for many Americans,” the blog from Health and Human Services states. “Some have had trouble creating accounts and logging into the site, while others have received confusing error messages, or had to wait for slow page loads or forms that failed to respond in a timely fashion. The initial consumer experience of HealthCare.gov has not lived up to the expectations of the American people. We are committed to doing better.”

Officials also said they had called in people in the tech field outside the government to help, though they would not specify from where, and that they would like feedback from consumers as they experience problems in the system.

The blog followed remarks from Treasury Secretary Jack Lew on NBC’s Meet the Press Sunday saying officials are working around the clock to fix the problems, as well as the announcement of an event Monday at the White House focusing on health care.

A White House official, speaking on condition of anonymity in advance of the event, said the president will discuss the health care law and address the technical issues directly.

“I think that there’s no one more frustrated than the president at the difficulty in the website,” Lew said.

While there was some good news about the exchanges this weekend — half a million people were able to apply for insurance, which means they filled out a form with their basic information and have either received or are waiting for their eligibility determination for tax subsidies or Medicaid enrollment — much of the news focused on admitting that what was advertised as a simple way to sign up for health insurance had become a fiasco of error messages, wait times and shutouts from the system.

The blog cites specific areas that need to be fixed. Officials say the problem is software coding issues. The data hub, which allows the government to determine who is eligible for credits, works, the blog states. State officials who created their own exchanges concur that this portion of the system works. That means the problem is with healthcare.gov — the federal exchange website itself.

Douglas Holtz Eakin, former director of the Congressional Budget Office and former chief economic policy adviser to the 2008 presidential campaign of Sen. John McCain, R-Ariz., said he’s not surprised that the launch was rocky because the companies who would profit from the market — the insurers — were not involved in setting up the technology to ensure the process went smoothly.

“This is an attempt to build a nation-wide market trading system where the exchange has no financial incentive and it’s failing miserably,” he said. “What you hear are assessments that are uniformly negative. This is not a system capable of doing what you envisioned.”

The government has had to update the site several times with new coding to try to fix bugs, which has led to some new problems as people had to refresh their computer cache so the “cookies” that contain personal data wouldn’t link back to areas that no longer existed. Those who have begun the enrollment process in the past few days seem to have had a better chance of finishing an application than those who tried in the first week, many of whom still haven’t been able to enroll.

Officials still maintain that the volume of visitors beginning Oct. 1 stressed the system. To try to fix the problem, people were sent to a “waiting room” or received a message that told them to wait until the site was ready for them, “but many found this experience to be confusing,” the blog states.

So they added more capacity so people could sign up.

“We’re proud of these quick improvements, but we know there’s still more work to be done,” the blog states. “We will continue to conduct regular maintenance nearly every night to improve the experience.”