Many older smokers and former smokers should undergo annual CT scans for lung cancer, an influential health panel recommended for the first time Monday, suggesting that early detection of the leading cause of cancer deaths could save more than 20,000 lives every year.

The draft recommendation, by the U.S. Preventive Services Task Force, said people aged 55 to 79 with a lengthy history of at least moderate smoking should be screened if they have smoked in the past 15 years. That population is most at risk for lung cancer and would get significant benefits while experiencing relatively little harm from the low-dose radiation used in chest CT scans, and from false positive tests, the panel said.

“Right now, about 160,000 [people] die from lung cancer each year,” said Michael LeFevre, the task force’s co-vice chairman. “That’s more cancer deaths than from colon, breast and prostate cancer combined. . . . We could prevent 14 percent of those deaths.”

Patient advocates welcomed the task force’s decision to give its recommendation a “B” rating, which, under the terms of the Affordable Care Act, would require insurance companies eventually to cover the tests without co-payments from patients. The average national cost of the procedure is about $750, though prices vary widely, according to Castlight Health, which analyzes price and quality data for health-care services.

A spokesman for the Department of Health and Human Services said that if the recommendation becomes final after a public comment period, coverage would begin no sooner than a year later, with the start of each new insurance plan year. So if the recommendation were finalized by the end of 2013, coverage would go into effect at the start of a plan year that begins in January 2015.

A spokesman for Medicare said the program would need to determine whether the service is covered.

“The link to the Affordable Care Act is a very big deal,” said Robert Smith, director of cancer screening for the American Cancer Society. He predicted an increase in physician referrals for lung cancer tests as a result of the new recommendation.

Another group, the Lung Cancer Alliance, went further. Its president and CEO, Laurie Fenton Ambrose, called the recommendation a “monumental moment” in the battle against lung cancer.

The task force, an independent panel of experts that issues recommendations to health-care providers, the federal government and the public, determined nine years ago that there was not enough information to recommend routine lung cancer screenings for smokers or former smokers. About 85 percent of all lung cancers are attributable to first- and secondhand tobacco smoke.

But in 2010, the National Cancer Institute released the results of the National Lung Screening Trial, which compared the effectiveness of low-dose CT scans with chest X-rays in detecting cancer among more than 53,000 current and former heavy smokers. The study showed that those who received CT scans had a 20 percent lower risk of dying from lung cancer.

A CT scan provides a three-dimensional image of the lungs, and a chest X-ray produces a single two-dimensional image. A scan is more likely to spot a tumor when it is small and easier to remove surgically.

About 90 percent of people with non-small cell lung cancer, the most common type, die. But the task force noted that when the cancer is caught at its earliest stage, median five-year survival is 77 percent. Once the cancer has spread to areas near the lungs, survival drops to 25 percent, and to just 4 percent when the cancer metastasizes to other parts of the body.

In developing its recommendation, the task force produced a model that balanced the benefits of the test against the potential harm from the low-dose radiation of CT scans and from follow-up scans, X-rays and biopsies that it acknowledged doctors would perform as a result of the many “false positive” tests the scans produce.

Panel members settled on 55 as the minimum age for screening for anyone who has a “30 pack-year” smoking habit and has smoked in the past 15 years. A pack-year is a pack-a-day habit for 30 years or a two-pack-a-day habit for 15 years.

The panel’s model suggests that screenings of such people would avert 521 lung cancer deaths per 100,000 smokers but cause 24 as a result of radiation exposure. LeFevre noted that deciding whether to undertake many medical procedures requires that kind of cost-benefit analysis and that it will be the responsibility of primary-care physicians to assess the benefits of screenings for individual patients. The recommendation calls for physicians to use “caution” in recommending screening to patients, especially older smokers, with other illnesses.

Other experts differed on the risks of the recommendation. Howard Forman, a professor of diagnostic radiology and public health at the Yale School of Medicine, said that while he is generally conservative about exposing patients to radiation from CT scans, “there is no definitive evidence at this dose level that we are actually causing harm.”

“I personally think that the risk is there, but we don’t know that it’s there,” he said.

Kenneth Lin, an associate professor of family medicine at the Georgetown University School of Medicine, worried that the recommendation covers too broad a group and would lead to over-diagnosis, too many screenings and needless procedures such as biopsies.

Even smokers with the highest risk have only a one in 100 chance of preventing a fatal lung cancer through the test, Lin said. He said he hopes to see the recommendation narrowed after it receives public comment over the next four weeks.

But overall, the recommendation drew positive reaction from experts, who said that screening could have more impact on lung cancer deaths than anything other than quitting smoking or never starting.

“The message from a report like this is that, for the first time, there seems to be a benefit that outweighs harm in getting lung cancer screening, for a select population,” said Albert A. Rizzo, past chairman of the board of directors of the American Lung Association.