For British newspapers, any sort of misbehavior on the part of members of the royal family is fair game -- alcohol, promiscuity, bedroom squabbles, Princess Di's refusal to give birth in the palace. But reports of biopsies of breast lumps, even though they turned out benign, for members of the British royalty never have received even oblique allusion in the British press. Word has been whispered by British oncologists to their American colleagues here, yet it is not fodder for Fleet Street.

In this country it has been pretty much the other way. Scandal may in the past have been suppressed, but tissue sections have long been emblazoned on front pages all over the country.

Speaking of the publicity attendant on Nancy Reagan's modified radical mastectomy last week, Bartholomew Collopy, associate for ethical studies at the Hastings Center, said that "from her point of view it is a private and personal decision, no doubt about it, but there is the typical problem of someone who is a public figure where everybody is interested. I think it is unfortunate, in a way, especially when, as in this case, you're not even talking about an officeholder.

"Still," said Collopy, "I guess it is naive to think that we're going to back away and allow them to have their privacy."

The Hastings Center is the New York think tank that specializes in studies of medical ethics. Collopy was asked to comment both on the public attention paid the first lady's choice of treatment for the lesion in her left breast and on the comments of physicians not directly connected with her case.

Because the first lady chose to keep private most of the information surrounding her case, and because some of the top specialists at the National Cancer Institute were not immediately accessible, her treatment became a subject of some controversy even before the results of the final biopsy were known.

"I think it is unfortunate for medical people who might not know all the facts, details and the decision-making processes to comment on it from the outside," Collopy said. "It probably does not help the exaggerated attention that she would get in any case.

"Changing forms of medical practice is often a matter of changing public perception. We really do not know what information she was given, whether she was fully informed or the decision was paternalistically induced by her physician, which would make it even more lamentable, if that were the case." Then he said, "But there I go doing the same thing. It is making a diagnosis behind a curtain."

Breast cancer patient and patient-rights activist Rose Kushner, who herself rejected a radical mastectomy a dozen years ago and helped speed the change in medical practice that saw it all but eliminated, recalls that "Betty Ford's radical mastectomy set that movement back a few years." First ladies are role models, and "I've had hundreds of calls from women who are worried now that their lumpectomies were ill advised."

Said Collopy, "I think it doesn't hurt for the politics of this issue for physicians to come out clearly and say, 'If this in fact is all that she had, I might not have recommended this.' It seems to me that the question of public perception in this area is then somehow protected. But," he added, "they would have to add the caution that 'This isn't my patient and I don't know all the elements that entered into the decision.'

"Then they would protect her privacy and keep the public informed at the same time about what is going on in medicine, particularly in this area."

Press preoccupation with the minute details of presidents' (and first ladies') medical ills probably stems from the to-do over President Eisenhower's ileitis that saw almost hourly reports of his intestinal functioning. Lyndon Johnson's gallbladder operation got similar attention, aided by LBJ's eagerness to show his scar to the world.

Before then, it was anybody's guess. In "Medical Cover-Ups in the White House" by Dr. Edward B. MacMahon and Leonard Curry, the authors offer such medical lore as:

James Garfield was not assassinated after all. He was shot, but actually died of a heart attack exacerbated by infection introduced by his doctors as they searched for the bullet.

Grover Cleveland had secret surgery performed on what was believed to be cancer of the jaw. It was performed aboard a yacht to maintain the secrecy.

Franklin Roosevelt may have suffered many less serious cerebral hemorrhages before the fatal one in 1945. They were either misdiagnosed or covered up.

The Reagans are taking the public curiosity about their inside stories with humor and aplomb. Earlier this week, they revealed plans to exchange as Christmas gifts framed copies of their medical diagrams as seen in the media.