There is little to no evidence that circumcision protects men who have sex with men from infection.

Another reason circumcision would have less of an impact in the United States is that some 79 percent of adult American men are already circumcised, public health officials say.

But newborn circumcision rates have dropped in recent decades, to about 65 percent of newborns in 1999 from a high of about 80 percent after World War II, according to C.D.C. figures. And blacks and Hispanics, who have been affected disproportionately by AIDS, are less likely than whites to circumcise their baby boys, according to the agency.

Circumcision rates have fallen in part because the American Academy of Pediatrics, which sets the guidelines for infant care, does not endorse routine circumcision. Its policy says that circumcision is “not essential to the child’s current well-being,” and as a result, many state Medicaid programs do not cover the operation.

The academy is revising its guidelines, however, and is likely to do away with the neutral tone in favor of a more encouraging policy stating that circumcision has health benefits even beyond H.I.V. prevention, like reducing urinary tract infections for baby boys, said Dr. Michael Brady, a consultant to the American Academy of Pediatrics.

He said the academy would probably stop short of recommending routine surgery, however. “We do have evidence to suggest there are health benefits, and families should be given an opportunity to know what they are,” he said. But, he said, the value of circumcision for H.I.V. protection in the United States is difficult to assess, adding, “Our biggest struggle is trying to figure out how to understand the true value for Americans.”

Circumcision will be discussed this week at the C.D.C.’s National H.I.V. Prevention Conference in Atlanta, which will be attended by thousands of health professionals and H.I.V. service providers.

Among the speakers is a physician from Operation Abraham, an organization based in Israel and named after the biblical figure who was circumcised at an advanced age, according to the book of Genesis. The group trains doctors in Africa to perform circumcisions on adult men to reduce the spread of H.I.V.