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The White House went on defense Wednesday about new government findings that advise against routine mammograms for women under 50, saying the guidelines are merely a recommendation and that the U.S. Preventive Services Task Force that produced the report out this week has "no power" to deny health care coverage.

But while the task force doesn't dictate coverage, critics say findings from the group could influence federal policy as Congress considers plans to overhaul the health care system.

"This is the way rationing, which my colleagues and I have warned about, will begin to enter the market place -- slowly, imperceptibly and lethally," Republican Rep. Marsha Blackburn said in an e-mail to FoxNews.com.

Blackburn, of Tennessee, joined other Republican women in Congress on Wednesday to speak out in opposition to guidelines that recommend changing when and how women should be tested for the No. 2 cancer killer in women.

White House Deputy Communications Director Daniel Pfeiffer blasted critics of the guidelines in a blog posted to the administration's Web site late Tuesday, taking particular aim at an article posted on FoxNews.com.

"One of the hallmark tactics from opponents of health insurance reform has been to grab onto any convenient piece of information and twist it into some misguided attack on reform -- no matter how unrelated it may actually be," wrote Pfeiffer. "Today they're going back to that playbook again, and Fox News obliges them."

In a Q&A developed for the Web site, Pfeiffer wrote that under the health insurance reform being considered in Congress, the USPTF does not have the power to deny insurance coverage but "their recommendations would be used in health reform to identify effective clinical preventive services."

"While the bills are still being drafted and debated in Congress, health insurance reform legislation generally calls for the task force's recommendations to help determine the types of preventive services that must be provided for little or no cost. The recommendations alone cannot be used to deny treatment," he wrote.

Health and Human Services Secretary Kathleen Sebelius added Wednesday she does not believe the recommendations by the U.S. Preventive Services Task Force would alter insurance coverage.

"The U.S. Preventive Service Task Force is an outside independent panel of doctors and scientists who make recommendations. They do not set federal policy and they don't determine what services are covered by the federal government," she said.

The USPSTF, which reports to the Department of Health and Human Services, released its updated 2009 guidelines on Monday. It recommended against routine screening of women aged 40 to 49 years -- despite acknowledging evidence in the report that mammograms have reduced the mortality rate in younger women.

The task force advises that women aged 50 to 74 receive mammograms every other year and recommends against teaching breast self-examinations.

The panel says the recommendations apply to women 40 years or older "who are not at increased risk for breast cancer by virtue of a known underlying genetic mutation or a history of chest radiation."

In response, the American Cancer Society issued a statement Tuesday saying it still recommends annual mammograms for women 40 and over.

"Our experts make this recommendation having reviewed virtually all the same data reviewed by the USPSTF, but also additional data that the USPSTF did not consider," ACS said. "The USPSTF says that screening 1,339 women in their 50s to save one life makes screening worthwhile in that age group. Yet USPSTF also says screening 1,904 women ages 40 to 49 in order to save one life is not worthwhile. ... With its new recommendations, the USPSTF is essentially telling women that mammography at age 40 to 49 saves lives; just not enough of them."

But Dr. Cathleen London, a family physician and clinical instructor at Boston University and Tufts School of Medicine, said routine screening of low risk women under 50 is unnecessary -- and often leads to false-positives. London said breast tissue is more dense in women in their 40s who have not yet undergone menopause.

"Let's be clear: We are talking about routine screening -- we're not talking a woman who comes in with a lump," she said.

The independent government panel of doctors and scientists has insisted that the cost of such preventive testing was not a factor in its assessment of breast cancer screening.

"These recommendations have nothing to do with any kind of analysis that addressed cost effectiveness," Dr. Diana Petitti, vice chairwoman of the panel, told CBS News in an interview Tuesday.

"Cost effectiveness was not a part of the discussion. Cost was not uttered in the room," she said.

But costs were referenced at least three times in the panel's report when assessing common types of breast cancer screenings, including clinical breast examinations, film and digital mammographies, and magnetic resonance imaging -- or MRIs.

"Digital mammography is more expensive than film mammography," the guidelines note, while MRIs are "much more expensive" than either film or digital mammography.

"They [the White House] want to say that you can't connect those dots," said Rep. Phillip Gingrey, R-Ga., a practicing obstetrician and gynecologist for 26 years. "We clearly can connect them."

Gingrey and others say they fear insurance companies will seize upon the guidelines to deny coverage to women under 50 who do not have an increased risk for harmful genetic mutations -- like BRCA1 or BRCA2, genes that when mutated have been linked to breast cancer.

"The White House can deny all day long but eventually the denial will be for patient care and this is known as rationing," he said.

"Mammograms and other preventive screenings should be provided on demand and in consultation with a doctor, not doled out on the recommendation of a distant panel in Washington," added Blackburn.

Sebelius said she recommends women continuing doing what they are doing -- consulting their doctors on what's best for them. She added that the task force "has presented some new evidence for consideration but our policies remain unchanged."

"I would be very surprised if any private insurance company changed its mammography coverage decisions as a result of this action," she added.

In supporting its argument against routine mammograms for women under 50, the task force notes "potential harms" of mammography testing, including anxiety, distress and additional "invasive procedures" like biopsies or fine-needle aspirations that may come as a result of false-positives.

"False positives are common with mammography and can cause anxiety," the report states.

Rep. Phillip Roe, R-Tenn., a retired obstetrician and gynecologist, said the benefits of mammograms far outweigh potential "burdens" or "harms" that may come as a result of the screening.

"No one ever died of extreme anxiety. People die of breast cancer," he said.

But advocates of the new recommendations say they hope they will lead to more efficient testing methods.

Dr. Eric Braverman, a clinical assistant professor of integrative medicine at Cornell Weill Medical College in New York says mammograms are not nearly as effective in detection as some other tests, like MRIs and ultrasounds.

"I'm not impressed by mammograms in general," said Braverman, who called manual examinations a "total failure."

"I support the new guidelines because I think it will lead to better testing. [The ultrasound] is a better screening procedure that's safer and easier and picks up things fast," he said, adding that he thinks women should receive ultrasounds as part of their routine medical exams, beginning at an early age.