Brain damage and unusual changes in spinal fluid have been detected in more than two dozen Swedish radar-maintenance workers exposed for 10 years or more to microwave radiation, according to a researcher at Sweden's University of Goteborg.

The study provides some of the first evidence of physical changes directly linked to microwaves, to which most people are exposed at levels 10,000 to 100,000 times below what the radar operators experienced. It has major implications not only for radar workers but also for the increasing numbers of people in general who are exposed to microwaves and other forms of non-ionizing radiation.

Non-ionizing radiation is generated by electrical and magnetic fields that alternate at varying frequencies. Its uses range from radio and television to sophisticated radar missile-tracking stations to overland power lines, video display terminals, microwave ovens, garage-door openers and cellular telephones.

"This is a very serious problem," said Dr. Robert O. Becker, a retired researcher, who describes the effects of non-ionizing radiation in a book, "The Body Electric."

"I think that it's more important than the chemical contamination of the environment that Rachel Carson wrote about in 'Silent Spring,' " he said.

For 40 years controversy has been brewing about whether non-ionizing radiation poses health risks, much the way scientists once debated the dangers of ionizing radiation, such as X rays and radiation from nuclear explosions.

"The Swedish study is another in a long line of studies that suggest a problem," said Andrew Marino, a biophysicist at the Louisiana State University Medical School in Shreveport who was a consultant on a study for the Navy on the health and environmental effects of extremely low frequency (ELF) radio waves, a form of non-ionizing radiation. "It's not proof, but it raises a clear warning of a present danger."

Dr. Hans-Arne Hansson, a Swedish neurologist who teaches at the medical school at the University of Goteborg, reported that extensive tests showed that the radar workers, men aged 35 to 62, displayed symptoms of brain damage known as frontal lobe brain syndrome and had disabilities ranging from memory loss and difficulty concentrating to such severe mental impairment that they have been forced to quit.

In addition, Hansson, who will publish these findings this year in a peer-reviewed scientific book, discovered an abnormal protein in the spinal fluid of these workers -- a protein that "may be the first step towards having a marker for overexposure to microwaves," according to Thomas C. Rozzell of the U.S. Office of Naval Research -- London.

This protein seems to be the human equivalent of an abnormal substance Hansson has isolated from the spinal fluid of rabbits exposed to microwaves in experiments.

"Hansson is the one person who has shown objective changes of cells in the brain with exposure to electromagnetic radiation," said Becker. "That's the kind of smoking gun you need in this field."

The presence of this abnormal protein in the spinal fluid appears to signal "trouble in the brain," said Dr. Ross Adey, associate chief of staff for research and development at the Veterans Administration Hospital in Loma Linda, Calif. "The protein that Hansson sees is an indication that the normal balance between two cell types in the brain has been seriously disturbed and that a defect in nerve-cell function is inevitable."

Neurons in the brain "depend for their good health on neuroglial cells," Adey said. "Neuroglial cells are the guardians and the custodians of much of the metabolic activity" of other brain cells. The abnormal protein described by Hansson is thought to be derived from neuroglial cells, Adey added.

Hansson's findings help "set in perspective other work that has been done by Dr. Bernard Servantie of the French Navy" and by Polish researchers, Adey said.

Called PI 4, the protein has been found only in people with substantial exposure to microwaves. It cannot be accounted for by "other possible causes of disease or health problems," Hansson reported. Men similar to the radar workers except for a lack of microwave exposure showed no evidence of the protein or the other brain damage.

Despite an extensive search of several thousand samples of spinal fluid, the protein also "has not been demonstrated in patients with other various neurological symptoms" caused by tumors, injury, nerve damage or multiple sclerosis, Hansson said in a telephone interview.

The radar workers also showed alterations of normal proteins in the spinal fluid and, in two cases, partial blindness caused by retinal damage.

These and other findings will be presented in June at the annual meeting of the Bioelectromagnetics Society in San Francisco. The results have circulated in recent months in unclassified reports among the U.S. military scientific community. They could have particular significance for military personnel and for others with chronic occupational exposure to microwaves, such as people who service telephone microwave relay stations.

Hansson has suggested that the findings indicate that "exposure of nervous tissue to electromagnetic fields ranging from power line frequency to microwaves may thus exert a wide range of effects, mostly by mechanisms we know little about." He reported that "microwave exposure may induce chronic effects of nervous tissue which may become evident after a 'silent period' " lasting months or years.

Results of these studies "suggest that even humans occupationally exposed to microwaves of moderate to high intensity could be at risk of brain damage," Hansson said.

These findings have special importance in the United States, where allowable exposure to microwaves and other forms of non-ionizing radiation is among the world's highest. A 1982 study by the Occupational Safety and Health Administration estimated that 9 million Americans are exposed to microwave radiation. With the heavy use of radar, virtually "everyone in the Navy is exposed to potentially high levels of microwave radiation," said a scientist from the Office of Naval Research.

Studies from around the world are beginning to suggest that this "electropollution" common to modern life may produce significant biological changes. "We're finding more and more effects every day from electromagnetic fields," said Rozzell of the Office of Naval Research. "Strange little effects are cropping up. Animal studies are pointing out that at very low levels one is quite likely to see some biological effects, which may or may not be harmful."

Two recent studies -- one of Polish military personnel, the other a U.S. Air Force-sponsored animal study -- also suggest an increased risk of cancer.

"When you turn on your television it's not little green men that are bringing the picture to you," Becker said. "It's electromagnetic waves that are passing the picture."

Scientists once thought that non-ionizing radiation posed few health effects -- unless enough of it were absorbed to heat cells or tissues, an effect exploited in microwave ovens.

"My own personal opinion is that there have been enough reports in the scientific literature to indicate that there are some effects other than thermal effects," said Dr. Vincent Archer, a clinical professor of occupational medicine at the University of Utah Medical Center. "We don't have enough information to know how serious that non-thermal effect is."

Samples of spinal fluid were taken when microwave bombardment of the U.S. Embassy in Moscow from the 1950s to 1970s was revealed. "But that cerebrospinal fluid was not looked at in the kind of detail that Hansson has looked at," said Samuel Koslov, who assisted the medical team that examined the exposed embassy workers.

Exposure at the embassy was also "on the order of microwatts per square centimeter," 1,000 times less than the "milliwatts per square centimeter involved in radar testing," Koslov said.