Washington ? Women in their 40s should stop routinely having annual mammograms and older women should cut back to one scheduled exam every other year, an influential federal task force has concluded, challenging the use of one of the most common medical tests.

In its first re-evaluation of breast cancer screening since 2002, the independent government-appointed panel recommended the changes, citing evidence that the potential harm to women having annual exams beginning at age 40 outweighs the benefit.

Coming amid a highly charged national debate over health care reform and simmering suspicions about the possibility of rationing medical services, the recommendations immediately became enveloped in controversy.

“We’re not saying women shouldn’t get screened. Screening does saves lives,” said Diana Petitti, vice chairman of the U.S. Preventive Services Task Force, which released the recommendations Monday in a paper being published in today’s Annals of Internal Medicine. “But we are recommending against routine screening. There are important and serious negatives or harms that need to be considered carefully.”

The task force’s new guidelines, which also recommend against teaching women to do regular self-exams of their breasts and concludes that there is insufficient evidence to continue routine mammograms beyond age 74, immediately triggered intense debate.

Several patient advocacy groups and many breast cancer experts praised the shift, saying it represents a growing recognition that more testing, exams and treatment are not always beneficial and, in fact, can harm patients. Mammograms produce false-positive results in about 10 percent of cases, causing anxiety and often prompting women to undergo unnecessary follow-up tests, sometimes disfiguring biopsies, and unneeded treatment, including surgery, radiation and chemotherapy.

But the American Cancer Society, the American College of Radiology and other experts condemned the change, saying the benefits of routine mammography have been clearly demonstrated and play a key role in reducing the number of mastectomies and the death toll from one of the most common cancers.

“Tens of thousands of lives are being saved by mammography screening, and these idiots want to do away with it,” said Daniel Kopans, a radiology professor at Harvard Medical School. “It’s crazy — unethical, really.”

Some questioned whether the new guidelines, coming in the midst of a national debate about the health-care system and costs, were designed more to control spending than to improve health. In addition to prompting fewer doctors to recommend mammograms to their patients, they worried the move would prompt Medicare and private insurers to deny coverage of many mammograms.

The new recommendations took on added significance because under health care reform legislation pending in Congress, the conclusions of the 16-member task force would set standards for what preventive health care services insurance plans would be required to cover at little or no cost.

About 39 million women undergo mammograms each year in the United States, costing the health care system more than $5 billion a year.

Petitti denied that the panel was influenced by the health care reform debate or cost issues.

The new guidelines were based on a comprehensive analysis of the medical literature that included an update of a Swedish study involving some 70,000 women, new results from a British trial involving more than 160,000 women and data from more than 600,000 women from the U.S. Breast Cancer Surveillance Consortium.

In addition, the task force commissioned an unusual study funded by the National Cancer Institute that involved six independent teams of researchers conducting separate mathematical modeling studies of the risks and benefits of 20 different screening strategies.

While annual mammography for all women beginning at age 40 reduced the death rate from breast cancer by at least 15 percent, the modeling studies indicated that the added benefit of starting before age 50 was modest, the researchers concluded.

For every 1,000 women screened beginning at age 40, the modeling suggested that just 0.7 deaths from breast cancer would be prevented while 480 women would get a false-positive result and 33 more would undergo unnecessary biopsies.

“What isn’t in the model but is an issue is how many extra imaging tests are done to follow up on things that turn out to be falsely positive and the harm of the anxiety that goes along with that,” Petitti said. “Then there’s the whole other line of problems that come into play, which is where there are some breast cancers detected that grow very slowly and would never have killed you.”

Cutting back to biannual screening of women age 50 and older would maintain 81 percent of the benefits of screening annually while reducing by half the number of false positives, the computer modeling study estimated.