The idea that one cancer death is prevented for roughly 2,000 women screened “doesn’t mean anything until you’re the one,” said Dr. Jacques Moritz, director of gynecology at Roosevelt Hospital in Manhattan. “No doubt about it, I’m going to say, ‘Well, you really don’t need it,’ and they’re going to say: ‘You don’t understand. I’m getting the mammogram. I’m not going to take the chance to be the one person that has it.’ ”

Most of the doctors, however, said they would inform younger women that the recommendations said they did not need mammograms if they were low-risk. They said they would also point out that groups like the American Cancer Society and the American College of Obstetricians and Gynecologists are sticking to the earlier guidelines.

“If we don’t give them both views, they will not trust our judgments,” said Dr. Ozgul Muneyyirci-Delale, associate professor of obstetrics and gynecology at SUNY Downstate. Dr. Muneyyirci-Delale said she worried that the conflicting advice might add to negative feelings many women have about mammograms, because of the pain of the test, exposure to radiation or a general distrust of medicine.

A few doctors, however, could see benefits for some women.

Dr. Deborah Gahr, a gynecologist in private practice in New York, said the guidelines would make the estimated 10 to 15 percent of women who resist have mammograms more confident in their decision. “In a sense, that’s good,” Dr. Gahr said. “Nothing is black and white in medicine.”

Patients are already trying to figure out what the recommendations mean. Dr. Daniel Kopans, a professor of radiology at Harvard Medical School and a strong proponent of mammography, said “one woman came all the way from Bermuda and said, ‘I’m not sure if I should be screened.’ ”