Low levels of electricity generated by power lines or home appliances may cause cancer, but the evidence is too circumstantial to draw firm conclusions, the Environmental Protection Agency reported yesterday.

The report, representing preliminary conclusions by EPA scientists based on published studies, is the most significant government recognition so far of the theory that fields of electromagnetic radiation common to many American homes might be sources of cancer.

A finding that such a vital tool as electricity may be a potential health threat is unsettling to regulators and scientists.

The report's authors pointed out gaping holes in the research. It remains uncertain, for example, how electricity can mutate cells and whether the strength of exposure increases the chance of cancer, as it does in known chemical carcinogens.

"At this time it would be imprudent to suggest any type of public policy," said Erich Bretthauer, assistant administrator for EPA's office of research and development. There is no reason for homeowners to test for electromagnetic fields, Bretthauer said, although proximity to the source of dangerous

frequencies does appear to play a role.

Electromagnetic fields are a form of radiation created by anything powered by electricity, from switching stations to television sets. The radiation takes two forms: electrical charges and magnetic waves. The frequency of electric current common to American homes has long been thought too weak to injure human cells.

But recent studies of children and workers who register elevated incidence of cancer after exposure to household-level frequencies show "a consistent pattern or response which suggests -- but does not prove -- a causal link," said the report.

Several studies showed increased incidence of childhood leukemia, lymphoma and nervous system cancer in homes with certain wiring configurations that may have produced dangerous frequencies.

Two studies found increased rates of neuroblastoma and brain cancer in children whose fathers handle electricity-generating equipment at work.

Scientists working in the laboratory have measured the effects of electromagnetic fields on cells "consistent with several possible mechanisms of carcinogenesis," according to the report. But there is no evidence that the effect would create tumors in living systems, the EPA added.

Bretthauer said that while it is still unclear how electromagnetic fields could cause cancer, scientists believe certain frequencies may cause cells to mutate. Some scientists believe lower frequencies may be the most dangerous.

The EPA study will be reviewed by outside experts, the first step in what could be a five-year research effort to establish whether electricity does cause cancer and to what extent.