Top government technology officials told an acrimonious congressional hearing on Wednesday that they expected the website at the center of President Barack Obama's signature healthcare law to be working smoothly by the end of the month as planned.
The Obama administration is grappling with ways to help millions of Americans unable to sign up online and those who have lost health insurance in spite of the president's oft-repeated promise that people who liked their plans could keep them when the law took effect on Oct. 1.
In a sometimes confrontational hearing, Republican lawmakers accused the technology officials of not being candid about red flags that the HealthCare.gov website would not be ready to go live on Oct. 1.
There is growing pressure from Republicans—and even Democrats—for legislation that would let Americans keep existing plans, even if the policies do not comply with higher standards set in the 2010 Patient Protection and Affordable Care Act, also known as Obamacare.
(Read more: Summers: Obamacare has already helped economy)
Obama has promised Americans that the website will work for most people by the end of the month—a critical deadline for those who need to sign up for insurance benefits that would start on Jan. 1.
HealthCare.gov was supposed to be the main way of signing up for insurance, Obama promising it would be as easy to shop for new insurance plans as it is to buy airline tickets online.
But the website has been slow and error-ridden.
"We have much work still to do, but are making progress at a growing rate," Todd Park, the chief technology officer at the White House, told the Republican-led House of Representatives' Oversight Committee.
The website can now handle 20,000 to 25,000 concurrent users, Park testified—an improvement, but far short of the 50,000 to 60,000 that the system was originally designed to handle.
(Read more: Obamacare single-payer a ploy, says ex-GOP Senator )
The website is faster, and can now register about 17,000 people per hour in plans, he said.
Henry Chao, the deputy chief information officer at the Centers for Medicare and Medicaid Services, testified that officials are "working around the clock to address problems so that the site works smoothly for the vast majority of users by the end of this month."
The website's problems and the policy cancellations have provided powerful ammunition for Republicans, who see Obamacare as a costly expansion of government, say it is too complicated to work and will lead to higher healthcare costs.
The problematic rollout has also frustrated Obama's fellow Democrats, who worry it will be a major liability in their re-election fights. Some have called for a change in the law. There are a range of possible fixes to allow people to temporarily keep their plans, but many are logistically difficult, legally risky, or could undermine other parts of the law, according to policy experts.
(Read more: Bill Clinton: Obama 'honor' health-care pledge)
The White House had pleaded with the committee to postpone Park's appearance, saying he needed to devote all his time to fixing the website. But the committee's chairman, Darrell Issa, subpoenaed him, saying it was important to hear why the website launch was such a disaster.
"This wasn't a small mistake," said Issa. "This was a monumental mistake to go live and effectively explode on the launch pad."
The law aims to provide health benefits to millions of uninsured Americans. It mandates that most Americans be enrolled for health coverage by March 31 or pay a fine.
During the hearing, Elijah Cummings, the top Democrat on the committee, accused Issa of selectively disclosing documents and making untrue allegations.
"Nobody in this room, nobody in this country believes that Republicans want to fix the website," Cummings said.
Issa aggressively questioned Chao about whether the site protected Americans' personal information, such as their social security numbers.
Chao said it was safe. "To consciously know that it failed testing and then put it into production for people to use is not what we do," Chao said.
The security of the website has become another major target for Republicans. At a separate hearing on Wednesday, a U.S. cyber security official said HealthCare.gov has already suffered a number of cyber threats, including one attempted denial of service attack that seeks to overwhelm and take down the site.
(Read more: Group protests subpoena of Obamacare's IT chief)