WASHINGTON (Reuters) - The chief technology officer for the White House is willing to testify to a powerful oversight committee in the U.S. House of Representatives, but Todd Park is still too busy trying to fix the glitch-ridden Obamacare website to appear, the White House said on Thursday.

Republican Darrell Issa said he wants to hear from Park and other top Obama administration tech officials next Wednesday about why HealthCare.gov has performed so poorly, potentially preventing millions of people from enrolling in new online health insurance exchanges.

Issa, noting that Park was a "central leader" in the website's development, asked him to reconsider his decision by Friday or potentially face a subpoena compelling him to testify.

Park is open to meeting with Issa's staff informally in late November and would testify at a hearing sometime in the first two weeks of December, said Donna Pignatelli, the assistant director for legislative affairs in the White House Office of Science and Technology Policy.

"Because Mr. Park is currently occupied full time on the critically important work of improving the website for the millions of Americans seeking affordable health insurance options, his testimony needs to be scheduled at a time that is less disruptive to that work," Pignatelli said in a letter to Issa.

IT ENTREPRENEUR

Park's precise role in the website's insurance marketplaces is unclear, although he has been deeply involved in the round-the-clock effort to try to fix the bugs, occasionally sleeping on a mat in his office.

Before joining the Obama administration, Park was a successful healthcare IT developer, steering Athenahealth through a blockbuster IPO, and helping start another company, Castlight, which provides data on healthcare costs.

The 40-year-old helped build the original HealthCare.gov website in 90 days in 2010 when he was chief technology officer at the Department of Health and Human Services. The website then provided information about public and private insurance programs, sorted by zipcode.

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Elijah Cummings, the top Democrat on the House Oversight panel, chastised Issa for the threat and for ignoring Park's offer to testify in December.

"I am personally very concerned that the Chairman's actions may have a direct and negative impact on efforts to fix HealthCare.gov, which would aggravate the problem rather than help solve it," Cummings said in a statement.

Issa is a strong critic of the Obama administration. He has launched a number of probes, including one into the Internal Revenue Service's scrutiny of conservative groups seeking tax-exempt status, and a "Fast and Furious" investigation into a failed U.S. government sting operation involving gun running.

The hearing next week could shed light on what role various officials played in developing the site's technology. So far, the project appears to have been spread out among offices and federal contractors without strong oversight.

Other officials due to appear include Steve VanRoekel, chief information officer at the White House and Henry Chao, deputy chief information officer at the Centers for Medicare and Medicaid Services.

The Patient Protection and Affordable Care Act, President Barack Obama's signature healthcare law, was passed in 2010 and upheld by the U.S. Supreme Court last year. It requires most Americans to have health insurance beginning January 1 or pay a fine.

Republicans see the Democratic president's program as a costly expansion of government and fear Obamacare is too complicated and expensive to work.

(Additional reporting By Karey Van Hall; Editing by Xavier Briand and Ken Wills)