A new study in a British medical journal has stirred a passionate de- bate among doctors in Europe and the United States by asserting that mammograms do not prevent wom- en from dying of breast cancer or help them avoid mastectomies. The question is dividing experts and women's health advocates, many of whom acknowledge that they do not know what to think about the new report. For more than two decades, annual mammograms have been part of life for millions of wom- en, with the American Cancer Soci- ety and the National Cancer Institute urging women to have them. Experts are still digesting the new findings, which appeared in the Oct. 20 issue of the journal The Lancet, and few if any authorities in the..... .................................. Those studies that found benefits from mammography were flawed, say the investigators, Dr. Peter Gotzsche, director of the Nordic Cochrane Center in Copenhagen... ......... For example they criticize a Ney York study from more than a quar- ter of a century ago finding that women who never had a mammo- gram died of breast cancer at a rate 30 percent higher than those who had the test. (Of the 30,565 who were never screened, 196 died over an 18- year period; of the 30,131 who had the test, 153 died.) "The quality of the trials was very surprising because it is pretty low," Dr. Gotzsche said in a telephone in- terview. "Even if they are judged by yesterday's standards, the quality is low. In some cases, we know why that happened - these trials were conducted by people who were unfa- miliar with clinical trial methodolo- gy. They were run by enthusiastic clinicians." The researchers cite with greater approval a more recent study in Malmo, Sweden, that compared 21,088 women who had mammo- grams to 21,195 who served as con- trols. After nearly nine years, 63 women in the mammogram group had died of breast cancer, compared with 66 in the control group - an insignificant difference. The other study the researchers approved of, done in Canada, involved 44,925 wom- en who had mammograms and 44,910 who did not. There were 120 deaths from breast cancer in the screened group and 111 among the women who served as controls. Nor did mammography lead to fewer mastectomies, the investiga- tors say. In the Malmo study, for example, 424 women in the mam- mography group and just 339 in the control group had mastectomies. One reason may be that doctors ag- gressively treated some tiny tumors found in mammograms - tumors that might never have developed into cancer or might never have been noticed in a woman's lifetime.