People living near nuclear reactors do not have an increased risk of cancer, according to a major epidemiological study released yesterday by the National Cancer Institute.

The report contradicts previous scientific studies and the widely publicized claims of antinuclear activists that atomic power plants pose a health hazard. The study, which looked at decades of health records on 16 types of cancer from 107 U.S. counties near 62 nuclear facilities, was one of the largest and most comprehensive of nuclear power plant safety ever conducted.

"From the data at hand, there was no convincing evidence of any increased risk of death from any of the cancers we surveyed due to living near nuclear facilities," said John Boice, chief of the NCI's radiation epidemiology branch.

The researchers who conducted the study and others who reviewed the report said, however, that due to a number of limitations in the study's design, it could not serve as the definitive answer to the question of whether nuclear reactors are hazardous to their neighbors.

For example, the researchers studied data only on deaths from cancer and not total cancer cases. This, they said, might have made the analysis less sensitive to less serious health risks caused by low-level radiation, such as curable cancers.

Another drawback was that many of the commercial reactors under study began operating in the 1970s while the survey counted cancer deaths only until 1984. Because of the long latency of many types of cancer, this raises the possibility that cancers caused by radiation from the plants may be in progress but that it is too soon for the victims to have died.

"A study like this, however large and comprehensive, cannot provide a final answer with respect to cancer risks from low-dose radiation," said American Cancer Society Vice President Clark W. Heath, a member of an outside panel of experts who reviewed the study. "This makes a substantial contribution, but I would not say this is the final answer."

The researchers said they are considering conducting follow-up surveys every five years.

Nuclear reactors are known to release consistent but small amounts of radiation during operation. According to the study, this amount is less than 5 percent of the background radiation exposure that people normally receive from the natural radioactivity in rocks and soil and from cosmic rays from the sun.

The NCI findings appear to contradict British studies in 1987 that seemed to show higher than expected childhood leukemia deaths around certain nuclear facilities in that country.

The NCI study was designed to see whether the British findings could be repeated in the United States. To do this the institute examined over 900,000 cancers deaths between 1950 and 1984 in 107 counties around and near all 52 commercial nuclear reactors in the United States that went into operation before 1982, as well as nine Department of Energy facilities and one commercial fuel reprocessing plant.

For each of the 107 counties studied, three other counties with similar populations, incomes and other socioeconomic factors -- but without nuclear plants -- were chosen for comparison. The study also compared cancer death rates in the study counties before and after the reactors were built.

The results showed that the risk of cancer was not any higher, on average, after a reactor was built than before, and that there was no statistically significant difference between cancer rates in counties with reactors and counties used as controls. In the case of leukemia, the type of cancer considered most likely to result from radiation exposure, children in the study counties were more likely to die from the disease before reactors were built than afterward.

The researchers, and some antinuclear activists, were quick to point out the limitations of the analysis. Ideally, for example, a analysis of the health risks of nuclear plants would focus only on the medical experiences of those people living downwind from the facility. But because such data are difficult to collect, the study looked at everyone in the counties, even those who might live some distance from the nuclear facility. This means that some potential dangers from low-level radiation could have been diluted by the experience of people not directly exposed to the plants.