Updated

Senators are calling on two independent government watchdogs to launch a "thorough investigation" into the failed launch of the ObamaCare website, as officials scramble to correct the problems by the end of the month.

The lawmaker leading the charge for the new probe is North Carolina Sen. Kay Hagan, one of several Democrats up for re-election next year who has been sharply critical of the HealthCare.gov launch. Hagan is circulating a draft letter, obtained by Fox News, that urges the Government Accountability Office and the inspector general for the Department of Health and Human Services to dig deep into what went wrong.

"These problems are simply unacceptable, and Americans deserve answers and swift solutions," the letter states. "Taxpayers are owed a full and transparent accounting of how the vendors contracted to build the site failed to launch it successfully. We strongly urge to you undertake a complete, thorough investigation to determine the causes of the design and implementation failures of healthcare.gov."

The letter poses a series of specific questions, including whether payments were withheld to any of the 55 contractors hired to build the site. The letter asks how projected costs have grown, and what the additional cost to taxpayers will be from bringing on contractors to fix the broken site.

Further, the letter asks why the contract was only opened up to a limited pool of contractors who originally bid on a 2007 contract.

The letter could get signatures from lawmakers on both sides of the aisle. Democrats like Hagan claim to still support the law's intentions, but have been highly critical of the administration over the launch.

Several moderate Democrats facing re-election next year have backed calls to extend the end-of-March deadline for individuals to obtain insurance coverage, citing problems with the main exchange site. The Obama administration so far has urged patience, claiming they plan to have the site fully functional by the end of November -- and has announced no plans to extend the March 31, 2014, deadline .

The Hagan letter states that once the site is up and running, "we expect that millions of people, for the first time, will not have to worry whether they can see a doctor because of a pre-existing condition, and other important market reforms will protect the insured from the prospect of unaffordable medical bills.

"In the meantime, it is critical that we understand how and why the mechanism for reaching that goal -- healthcare.gov -- failed to launch as required on October 1, 2013."

Meanwhile, emerging reports about the meager enrollments figures to date are fueling calls to delay the sign-up deadline.

According to an insurance industry report, fewer than 50,000 Americans have so far bought a private health care plan on the ObamaCare site, far short of the half-million enrollees the administration wanted the first month.

The Department of Health and Human Services, though, said officials could not confirm the numbers.

"We have always anticipated that initial enrollment numbers would be low and increase over time," said agency spokeswoman Joanne Peters. "And, as we have said, the problems with the website will cause the numbers to be lower than initially anticipated."

Sen. Orrin Hatch, R-Utah, top Republican on the Senate Finance Committee, said the numbers build the case for delaying the law.

"Whether it's higher costs, fewer choices or simply website glitches, it's becoming more clear with each passing day that this law isn't ready for prime time and should be delayed," he said in a statement.