They are best friends . . . confidantes, faithful companions when no one else is available. For millenia, pets have provided love and comfort to their human owners. Now there is growing evidence that they may sometimes be the prescription for better mental and physical health -- especially among the elderly, the disabled and the young.

In a workshop on pet therapy last week at the National Institutes of Health, researchers described how pets in certain circumstances can provide important health benefits, ranging from lowering blood pressure to alleviating depression.

"There are a group of studies strongly suggesting that contact with pets can transiently reduce heart rate and blood pressure," said Dr. Thomas Wolfle, deputy director of the NIH Office of Animal Care and Use. "Looking at, talking to and touching pets have been shown to be relaxing, particularly in comparison to interaction with other humans."

No one is saying that pets can cure disease. "Scientific research has failed to conclusively document a significant effect of pets for any human disease or condition," Dr. Alan Beck, director of the Center for the Interaction of Animals and Society at the University of Pennsylvania School of Veterinary Medicine, told the workshop.

Still, "there is some published evidence that contact with animals is associated with improved health in special circumstances," he said, and the evidence is strong enough to move pet therapy from the realm of an unproven medical treatment to one of limited help under certain conditions.

Further study is needed, researchers at the workshop recommended, to prove or disprove pet therapy's potential for more widespread health promotion uses.

"The rationale behind pet-facilitated therapy is a logical extension of the long-standing belief that animals are good, especially for children, the sick, the lonely and the elderly," said Beck. Where pets seem to be most beneficial is in buffering stress -- an important contributer to a wide variety of diseases. For children, "pets seem to serve as temporary emotional refuges during periods of unhappiness or distress," Wolfle said.

In the elderly, pets help alleviate depression and loneliness, particularly among those who have lost a spouse, relative or close friend. For individuals in wheelchairs, pets provide a special social entree.

"Disabled individuals {in wheelchairs} find it easier to converse, and other people feel less awkward interacting with them," Wolfle said, offering them a situation that "may improve the psychological and medical well-being of the handicapped individual."

Even among healthy college students, pets seem to have a beneficial effect.In a study of 92 college students, Uniformed University of Health Sciences researcher Cindy Wilson found that having a friendly but unfamiliar dog in the room lowered blood pressure.

The study, which will be published in an upcoming issue of the Journal of Nervous and Mental Disease, showed that this blood-pressure-lowering effect lasted even after the dog left the room. And while the reduction in blood pressure was significant but slight, "even lowering blood pressure one to two millimeters serves to improve health," Wilson said.

Throughout history, there has been a suspected link between animals and human health. "Primitive people thought that animals had special qualities of healing," said Dr. Leo K. Bustad, former director of the People Pet Partnership Program at the Washington State University College of Veterinary Medicine.

Pliny, the Roman writer and philosopher, prescribed lap dogs as comforters for women experiencing abdominal pains, Bustad said, and in the 1860s, mentally ill patients were given pets to care for as part of their therapy.

Clinical psychologist Boris Levinson of Yeshiva University in New York found in his work that having his pet dog in therapy sessions helped disturbed children communicate better.

Other scientific research on pet therapy reports that:

Pets provide an important source of comfort to young children, particularly in families where both parents work full-time outside the home and in families that move often. In a long-term study of 168 children, Dr. Brenda Bryant of the University of California at Davis found that pets "play a complex and rich variety of roles for children." They allow for greater freedom in sex roles, allowing boys to play a nurturer.

In addition, pet-owning children were more empathetic, calmer and more likely to be chosen as a confidante of other children than nonowners. Pet owners were also more able to accept help from others.

In nursing homes, pets seem able to help withdrawn elderly residents begin to participate in life again.

"These people smile more often, talk more and reach out toward people and objects more often when pets {dogs and cats} are present," said Dr. Susanne Robb, a quality assurance coordinator for the Veterans Adminstration.

"They show more attentiveness, more well-being and less depression, although there is no real improvement in their physical status."

Pets also may help heart disease sufferers recover. In a study of coronary care unit patients hospitalized for either a heart attack or for the severe chest pain known as angina, Dr. Erika Friedmann of Brooklyn College of the City University of New York found that pet owners were more likely to be alive one year after they were discharged than were nonowners.Today, slightly more than half of American households include a pet, according to a mail survey conducted in 1983 for the American Veterinary Medical Association. Pets are most likely to be owned by families and by couples whose children are 18 or older and have left home.

But despite their popularity and their potential health benefits, pets also have some significant drawbacks. "Risks associated with pets are real and substantial in terms of transmittable disease, trauma, allergies and cost," Wolfle said. The biggest hazard: animal bites. Estimates are that 500,000 to 1 million Americans are bitten by pets each year, more than three quarters of them by dogs, according to Dr. Peter Schantz, an epidemiologist with the Centers for Disease Control.

Pet bites are so common -- and often so severe -- that they account for approximately 1 percent of all visits to hospital emergency rooms in the United States, Schantz told the workshop.

For this reason, pets used for therapy in nursing homes, prisons and other institutions must be selected carefully, experts said. But when pet therapy is carefully monitored, the risks can be reduced. In a year-long study of nursing homes in Minnesota, Dr. Robert Anderson and his colleagues found that pet-associated illness and injuries were infrequent and could be minimized with advice and consultation by veterinarians and physicians.

"The U.S. Census should begin to include questions on the number and type of animals in people's homes," University of Pennsylvania's Beck proposed. "If this were done, we could begin to address a wide variety of public health issues . . . Just as coffee, tobacco and alcohol consumption are considered important because they alter the risk of many diseases . . ., we must be alert to the health-promoting potential of pet ownership."