Ongoing breast cancer research is finding more effective and less traumatic methods of diagnosis and treatment every day, although sometimes it takes years for the new findings to make their way into the everyday practices of surgeons and cancer specialists.

The mastectomy performed Saturday on Nancy Reagan has highlighted the fact that controversy persists over how best to treat this disease.

In one current research project, cases apparently similar to that of Mrs. Reagan are being treated with minimal surgery alone -- a lumpectomy -- sometimes without even looking at the axillary (underarm) lymph nodes. Half of the patients in this part of the National Surgical Adjuvant Breast Project are receiving lumpectomy alone, and half are receiving lumpectomy with radiation.

The project, directed by University of Pittsburgh surgeon Bernard Fisher, is still recruiting patients for the 2-year-old project, so no official results are available. However, word has been trickling out at meetings that for these lesions, the less traumatic treatment -- without radiation -- may be as effective in terms of long-term survival as lumpectomy with radiation.

For years there has been a school of thought that lesions smaller than a centimeter and confined to a milk duct are in fact not cancer but a pre-cancerous condition. If left untreated they would likely develop into cancer eventually, but a virtual cure is achieved by their simple removal.

Breast cancer will strike 130,000 American women this year, and ultimately one woman in 10 will face such a diagnosis. It is the second-leading cancer killer of women, after lung cancer.

Here are some common questions and answers about diagnosis and treatment:

Are breast cancers discovered more often by mammograms or by self-examination?

Fewer than 5 percent of breast cancers are discovered at a stage as early as Mrs. Reagan's -- when it is still too small to be felt. More than 70 percent are discovered by women examining their own breasts.

A recent poll conducted by Gallup for the American Cancer Society found that only about 15 percent of women have mammograms at all.

Does this procedure increase the chance of survival?

A mammogram-discovered cancer has a

far greater chance of being cured than those already large enough to be felt. For the type of lesion found in Nancy Reagan's breast, the cure rate is close to 100 percent.

Who is at risk of getting breast cancer?

Post-menopausal women, women who had their first babies after age 30, and women with a family history of breast cancer are at greatest risk.

Why don't all post-menopausal women have yearly mammograms?

Mammograms are often expensive -- ranging in price from about $50 to $150 each, and Medicare does not cover their cost as a routine screening device. To a woman in her late sixties living on Social Security, routine mammograms may seem a luxury. Two bills pending in Congress, one in the Senate sponsored by Barbara Mikulski (D-Md.) and a similar bill in the House sponsored by Mary Rose Oakar (D-Ohio), would provide Medicare coverage for routine screening mammography.

Does mammography hurt?

Some women with very sensitive breasts complain that the mammography process, during which the breast is slightly compressed, is painful. Usually a word to the technician will permit an adjustment to make it less so. In any case, the process takes only a few seconds, and whatever discomfort there is disappears immediately thereafter.

How many kinds of breast cancer are there?

Breast cancer is a curiously capricious

disease, behaving differently in different women. Some tumors are more sensitive to hormone treatment than others; some cancer cells multiply more rapidly. Some are environmentally caused; some may be genetic. Scientists are only just beginning to be able to predict how an individual cancer may behave in different patients.

Does estrogen treatment to prevent osteoporosis increase the risk of breast cancer?

Post-menopausal treatment with estrogen has been linked to cancer of the lining of the uterus. But if estrogen is combined with another hormone, progesterone, such cancers rarely occur. For women who have had ovaries removed surgically, estrogen therapy seems to protect against heart disease. There is still a suspicion -- not proved -- that if a hidden cancer exists in a woman's system, estrogen therapy might activate it, but estrogen is not believed to cause breast cancer on its own.

What effect does age have on the chance of a successful recovery?

Breast cancer in pre-menopausal women, especially those under 40, spreads more rapidly than in older women, requiring more aggressive adjuvant treatment. Because new mammography equipment carries a much lower dose of radiation than that of only a few years ago, many specialists are recommending baseline mammograms in the early thirties for women who have strong family histories of breast cancer. The American Cancer Society recommends a baseline at age 35, mammograms every two years between 40 and 50 and every year after 50. Cancer may grow more slowly in older women, but it is still fatal if not stopped in time.