House Republicans and members of the health insurance industry are dismissing as a gross overstatement an Obama administration study -- released as debate gets underway to repeal the health care law -- that says as many as half of all Americans under 65 have a pre-existing condition that could threaten their access to health insurance.

The Department of Health and Human Services study, released Tuesday, concludes that somewhere between 50 million and 129 million non-elderly Americans have a pre-existing condition -- the kind of condition insurance companies can use to deny coverage. The study further found that 15-30 percent of people in good health are likely to develop such a condition within eight years.

"We as a nation can't afford to repeal the health care law," HHS Secretary Kathleen Sebelius said on a conference call Tuesday.

But an America's Health Insurance Plans spokesman said the HHS study creates a disconnect between conditions and coverage.

"It's exaggerating the number of people who are actually impacted by pre-existing conditions,"said AHIP spokesman Robert Zirkelbach. "Most people who are applying are getting policies."

Rep. Louie Gohmert, R-Texas, said the suggestion that so many millions would be hurt by the repeal is both wrong and "offensive."

The study Tuesday comes as the administration and Democratic allies in Congress fight back against GOP efforts to strip their landmark domestic policy achievement of the past two years. House members returned Tuesday to Capitol Hill to debate the repeal bill after a weeklong hiatus in activities due to the shooting of Rep. Gabrielle Giffords, D-Ariz., and 18 other people in Tucson. A vote is expected Wednesday.

While millions of Americans have pre-existing conditions, according to the administration, most have coverage. The actual number of Americans within the 50 million to129 million range cited by HHS who have been denied coverage is unclear. The study estimated that up to 25 million of them are currently uninsured, without breaking out the number of people who were rejected by insurance companies.

Asked for more information, HHS referred FoxNews.com to a House Energy and Commerce Committee study last fall. That report found 651,000 people were denied coverage by the four largest for-profit insurers in the three years before the health care overhaul passed.

AHIP opposed the health care law enacted last year and set to go into full force in 2014. A 2009 AHIP study found nine in 10 people under 65 are insured through their employers, which generally don't withhold health coverage over pre-existing conditions.

The study also found nearly nine in 10 people who apply for coverage in the individual market are accepted -- others can apply to public programs like Medicaid, Zirkelbach noted.

The HHS study also showed most people have insurance through an employer. However, the study showed a high proportion of those Americans have a pre-existing condition, and if they become self-employed or leave their jobs could face hurdles in getting coverage elsewhere.

The HHS study reported that millions suffer from access-jeopardizing conditions ranging from high cholesterol to hypertension to asthma to obesity. Those conditions can make workers cling to their jobs out of concern for their chances of obtaining coverage in the individual market, according to the administration.

The health care law would prohibit insurance carriers from denying coverage to sick people starting in 2014. It would also block them from capping lifetime benefits and charging the sick more money for premiums.

The health care law aims to lower the number of uninsured not just by imposing new restrictions on health insurance companies. It will require people to buy insurance starting in 2014 and provide subsidies to defray that cost for low-income Americans.

House Speaker John Boehner describes the repeal as an economic imperative. Democrats warn that doing so will have the unpopular effect of leaving millions without health insurance or affordable care.

In a statement released before the study came out, Boehner said it's a myth to claim Republicans don't want to enhance access to coverage for individuals with pre-existing conditions. He noted that a GOP proposal last year "fully funded and reformed high-risk pools and reinsurance programs to guarantee that all Americans, regardless of pre-existing conditions or past illnesses ... lowering costs for all Americans without piling more debt onto our kids and grandkids," he said in a statement.

Calling the repeal push a "huge mistake," Sebelius said the law will, over the next few years, give those citizens with pre-existing conditions the "freedom and security that comes with having quality affordable health coverage."

According to the study, the lower estimate of those with pre-existing conditions was calculated by looking at the number of Americans with conditions that make them eligible for high-risk insurance pools run by the states. The higher number, 129 million, was calculated by looking at those with conditions that, based on insurance company guidelines, could be used to deny someone coverage, or at least charge them a higher premium.

Zirkelbach acknowledged the need to reform the individual insurance market. But Republicans say the bill in its entirety does not accurately address problems in expanding affordable coverage and the law as written puts costly burdens on employers which could lead to job losses at a tenuous time for the economy. They widely oppose the individual mandate requiring Americans to buy insurance as unconstitutional.

Some Democrats have indicated a willingness to compromise and rework a few controversial provisions. That may be where the debate leads. Though the House may have the votes to pass the repeal bill, Senate Majority Leader Harry Reid, D-Nev., has vowed to block it in his chamber.

House Majority Leader Eric Cantor, R-Va., dared Reid to bring up the bill.

"If Harry Reid is so confident it (would) die in the Senate, he should bring it up," Cantor said Tuesday.