By Roberta Rampton

WASHINGTON, Nov 12 (Reuters) - A top White House technology adviser will testify at a congressional hearing on Wednesday about the troubled launch of the website at the heart of President Barack Obama's signature healthcare reform despite the administration's assertions that he was too busy.

The White House confirmed late on Tuesday that Todd Park, its chief technology officer, would comply with a subpoena to testify at a hearing of the Republican-controlled House of Representatives Oversight Committee.

The White House had asked to delay the hearing until December, saying that Park was too busy helping to fix the HealthCare.gov website, which Obama has vowed will be working smoothly for most people by the end of the month.

Technical problems with the website since its Oct. 1 rollout have prevented many Americans from enrolling in the health exchanges set up under the 2010 healthcare law, also known as Obamacare.

"The partisan subpoena issued by House Republicans on Friday was an unfortunate and unnecessary step since we made clear several times that Todd Park is willing to testify," said Rick Weiss, a spokesman for the White House Office of Science and Technology Policy.

"It wasn't a question of if, it was a question of when," Weiss said.

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

A sought-after speaker at IT conferences, Park is popular within the technology community. More than 1,200 allies signed a petition at lettoddwork.org calling on Darrell Issa, the Republican committee chairman, to postpone Park's testimony.

"No matter what side of the aisle you sit on, Todd is one of the good guys. Let him do his job," the petition said.

Park, 40, helped build the original HealthCare.gov website in 2010 when he was chief technology officer at the Department of Health and Human Services. At the time, the website provided information about public and private insurance programs, sorted by zip code.

Also slated to testify are Steven VanRoekel, the chief information officer at the White House budget office, Henry Chao, the deputy chief information officer at the Centers for Medicare and Medicaid Services, and Frank Baitman, chief information officer for HHS.