Biofeedback. It burst on the American consciousness a few years ago, and was, at once, either touted as the most wondrous medical technique yet, promising a drug-free cure-all for just about anything -- especially headaches, backaches, ulcers -- or scorned as just another fraud perpetrated on the unsuspecting ill. Or at best a gadget for useless games involving self-hypnosis.

Snake oil or magic?

In a way both -- and neither.

The human machine was programmed, oh so ingeniously to cope with the essentially physical stresses of early humanity. When confronted with danger, the caveman's body went into high gear in preparation of what was deemed in the early '30s as "fight or flight" by eminent Harvard physiologist Walter Cannon. This high gear involved stomach-tightening, cold hands clenched jaws, flowing adrenalin and other hormones, constriction of blood vessels here dilation, there. Pretty efficient for its day.

The trouble is, here we are some 50,000 years later and it doesn't take a prehistoric monster, obviously, to evoke "fight or flight," the human machine's emergency high-gear response. Just a surly boss, a whiny kid, a hostile spouse. Not a mention a late bus, the dog eating the homework, the oil bill, the car breaking down, raccoons in the chimney . . . the oil bill.

To make a long story short, the inappropriateness of the caveman response to today's non-physical stress-filled environment is causing a lot of people a lot of physiological trouble. Like migraine (and lots of other) headaches, gastric problems, including ulcers and colitis, low-back pain as well as possible immune-system damage, making the body more susceptible to almost any ills imaginable, including cancer.

Biofeedback experiments have been going on quietly for decades in one behaviorial medicine laboratory or another. Sometimes government agencies -- the Pentagon, for one -- have underwritten them. Early successes, especially in the treatment of migraine headaches, may have been blown out of proportion, but there were, and continue to be, successes, often remarkable, sometimes amazing. (The library, nevertheless, of at least one major newspaper still files information on biofeedback under "para-psychology," with ESP, ghosts and Dr. Rhine.).

Biofeedback is deceptively simple. The concept -- learning conscious control of autonomic functions -- is terribly seductive. And popular expectations were so high that there was a loud clamor for it among the aching masses.And echoed among practitioners (not all doctors), some eager simply to get in on the action and some genuinely seeking to help their patients.

Last weekend, in a quiet, private clinic in Baltimore county's rolling Greenspring Valley, a dozen or so experts gathered to exchange knowledge and techniques of biofeedback with some 80 colleagues from all over the country -- psychiatrists, psychologists, neurologists, internists, psychiatric social workers, at least one chiropracter and various other medically based professionals.

Co-sponsored by the John Hopkins Medical School and the Mensana Clinic where it was held, the conference was a crash course in biofeedback's proliferating medical technology and technique. From the latest $40,000 biofeedback consoles, to hints about the continuing breakthrough work of pioneers like Dr. Joseph Kamiya and Dr. Thomas Budzynski, the former one of its principal theoreticians, the latter the head of the Biofeedback Institute of Denver and a major technological innovator in the field. But there were also strong, repeated warnings that its misues can have negative consequences.

Biofeedback, basically requires a mechanism to monitor, amplify and translate subtle internal physiological events. When a patient understands the signals for what is happening inside, he or she can be conditioned to exert varying degrees of control, as in aborting a migraine headache by learning to warm the hands from the inside.

Dr. Nelson Hendler, psychiatrist, neurologist and owner-director of Mensana puts it this way: "Biofeedback is the amplification of subtle changes in either the autonomic or voluntary nervous system so that the subject can become aware of certain physical changes . . . affording the subject the opportunity of altering the responses he was receiving and was previously unaware of."

Or, a means for countering the body's inappropriate "fight-or-flight" response to personal crises of the day.

"Essentially," says Dr. Charles F. Stroebel, psychiatrist, chrono-biologist, lecturer at Yale and the University of Connecticut -- and past president of the Biofeedback Society of America -- "some 90 percent of people doing biofeedback in this country may be guilty of malpractice."

Not that Stroebel, who is also directior of research at the Hartford, Conn., Institute of Living, doesn't think it is a most useful tool. In fact, he recounts, he used it to get rid of his own disabling tension headaches. It has "enormous potential," he says, "If it is used in the correct light."

Dr. Seymour Diamond, head of the Diamond Headache Clinic in Chicago, also finds biofeedback useful, but warns that nobody "should treat a headache unless they're able to diagnose the problem first. I'm not making a critical indictment of the psychologists," he says, "but they'll take patients who are not diagnosed and treat them with biofeedback . . . they may miss a brain tumor."

Both doctors note that diet can play a major role in headaches, especially migraines. Says Stroebel, "Even the highly trained biofeedback subject who knows how to do thermal and lowered EMG feedback, if given one of the substances to which he or she is allergic, will go on and have a headache."

Stroebel, a major force in treating stress-related problems, said that individuals who are "significantly depressed" may not be good biofeedback subjects, nor are people on medications. The ones on hard drugs, he says, "are just looking for another doctor to write narcotics for them" and the minor tranquilizers like valium "chemically interrupt the various stress pathways you're trying to alter."

There also can be problems with so-called "symptom-substitution" when biofeedback may remove a symptom (headache, say), but because the underlying psychological conflict is unresolved, a new symptom (like irritable colon) may appear or get worse.

There are, nevertheless, a whole host of areas -- from bleeding gums to rehabilitating muscles after strokes, even to self-contraception -- in which biofeedback can now or eventually will be of significant help. But only when the therapist can exercise an educated judgement, medical diagnoses have been made and the equipment is sound.

It is, notes Dr. Hendler, a "good tool for certain things. The intent of the conference was not to promote it as a panacea, but to educate (professionals) about its use."

The Biofeedback Society of America is a good source of further information on the burgeoning use of the technique. Inquiries may be addressed to Francine Butler, PhD. -- C-268; Executive Direcotr, Biofeedback Society of America, University of Colorado Medical Center, Denver, Colo. 80262. CAPTION: Illustration, no caption, by Bernard Schoenbaum; Copyright (c) 1979, The New Yorker magazine, Inc.