– A UnitedHealth Group Inc. subsidiary accepted partial blame Thursday for the poor initial performance of the website designed to sign up millions of Americans for insurance under the federal health care overhaul.

But an officer of Minnetonka-based UnitedHealth’s Optum unit said at a congressional hearing that the company fixed its problems quickly and also warned the government about computer coding problems by other contractors.

The revelations came during a sometimes combative four-hour hearing of the House Energy and Commerce Committee that saw members exchanging barbs over the rocky launch of the major shopping portal for the Affordable Care Act, commonly known as Obamacare.

Thursday’s hearing was called to bring the website’s principal private contractors — Optum, CGI Federal Inc., Serco Inc. and Equifax Work Solutions — to account for their roles in the growing angst of Americans trying to buy coverage.

“We understand the frustration many people have felt,” Optum Vice President Andrew Slavitt told a packed hearing room.

In 2012, Optum acquired Quality Software Services Inc., which the government paid $85 million to help build the $500 million health care website. The federal site serves three dozen states but not Minnesota, which built its own MNsure portal.

Slavitt said Quality Software — known as QSSI — successfully delivered a data services hub that verifies customer information, such as citizenship, by sending computerized queries to various government databases. Where it tripped up was in the early operation of a registration and access management tool to let people establish Health.gov accounts and shop for insurance plans.

Slavitt acknowledged that this function was “overwhelmed” by thousands of people trying to register simultaneously when the website opened. One possible cause, Slavitt testified, “was a late decision [by the government] requiring consumers to register for an account before they could browse for insurance products.”

Republicans on the committee branded the removal of the anonymous shopping function as a cynical White House ploy.

“The browser was turned off to hide the cost of the system,” charged Republican Rep. Cory Gardner of Colorado. He likened the website launch to “trying to watch the Three Stooges in HD.”

Democrats countered that the House’s Republican majority was still trying to sabotage reform because it wasn’t able to defund or delay it in recent budget negotiations and a partial government shutdown. Democrat Frank Pallone of New Jersey referred to the hearing as a “monkey court.”

Between the name calling and phrase turning, Slavitt and three other contractors fielded a few questions from the committee. QSSI increased the capacity of its registration and access tool within a week of its launch, so that it now runs fine, Slavitt said.

QSSI reported problems

But he fueled the fire by saying QSSI found problems when it tested computer code written by other contractors. QSSI turned the information over to the government and the other contractors to fix. He also turned heads when he said he had tried to apply for health insurance through the website as an experiment and never got an e-mail confirming his enrollment.

Slavitt and CGI Vice President Cheryl Campbell both said the two weeks the government spent testing the integrated pieces of the website was a much shorter time frame than other undertakings the size and complexity of Healthcare.gov.

In one test the system crashed with only a few hundred people trying to use it, Campbell said.

Testing an integrated computer system from beginning to end would ideally occur well before its launch to give time to find and fix problems, Slavitt said. “Months would be nice.”

But as Republicans focused on next week’s grilling of Health and Human Services Secretary Kathleen Sebelius before the committee, members of both parties expressed concern that Optum, CGI, Equifax Work Solutions and Serco seemed strangely satisfied with their performance in the production of a website that one person called a half-a-billion-dollar “clunker.”

No one admitted doing anything wrong, noted Democrat Anna Eshoo, who represents California’s tech-rich Silicon Valley.

“We’ve got problems,” she said. “There are thousands of websites that handle [simultaneous visits]. Amazon and eBay don’t crash the week before Christmas.”