Updated

Top government technology officials assured lawmakers on Wednesday that they are making progress in fixing the broken HealthCare.gov website, as doubts mounted about whether the administration can get the site running by the end of the month as promised.

U.S. Chief Technology Officer Todd Park, testifying before the House Oversight and Government Reform Committee, said they are making progress at a "growing rate."

"The team is making progress, the website is getting better each week," he claimed.

Henry Chao, the deputy chief information officer at the Centers for Medicare & Medicaid Services, also testified that the site is functioning "much better than it did initially," and can now handle 17,000 applications per hour.

He acknowledged, "we underestimated the volume of users" who would try to access the site, but claimed that the team has made a number of fixes since then.

But despite the assurances, ahead of the hearing The Washington Post reported that the ObamaCare website might not be fully functional by the end of the month -- despite pledges by President Obama to fix the site by then. The paper quoted one unnamed official as saying those working on the site have concluded the only way to handle the volume is to use other avenues to get people to sign up.

Rep. Darrell Issa, R-Calif., chairman of the House committee, charged Wednesday that the administration was cutting corners to meet "political deadlines" with the launch of the site.

"They weren't ready. They weren't close to ready. This wasn't a small mistake. ... This was a monumental mistake to go live and effectively explode on the launch pad," he said.

The hearing comes as the administration faces down critics, some from the president's own party, on another front. Lawmakers from both sides of the aisle have raised concern about the wave of cancellation notices going out from insurance companies, who have had to shift consumers onto different -- and sometimes more expensive -- plans in order to comply with the law.

The White House is vowing to address these concerns, without saying exactly what it might do.

But Bill Clinton added pressure on the administration to find a fix after he said in an interview Tuesday that Obama should "honor the commitment" that if Americans like their health plan, they can keep it.

After he spoke, California Sen. Dianne Feinstein, a prominent Democratic lawmaker, added her name to the list of lawmakers backing legislation that would reverse the cancellations by requiring insurance companies to continue to offer all current policies as of Dec. 31, 2013.

"I believe consumers should be allowed to choose their plans, and they should be adequately informed about those choices," Feinstein said.