Most advice and treatment for the four out of five people in this country who will eventually experience a backache or "pinched" nerve--7 million a year--result from erroneous diagnoses, claims New York physician John E. Sarno.

Among ineffective back remedies he lists:

* Bedrest. A lot of patients get worse in bed, says Sarno. The mother who is prevented from lifting a young child, for example, or a breadwinner worried about his job.

* Collars and corsets. They are designed to immobilize, but they don't even do that. There may be some brief placebo effect.

* Hard mattresses. Fine, if you like it, but "the idea that it has any therapeutic value is totally fallacious."

* Muscle relaxants and anti-inflammatory drugs: "The first work on the brain, not the muscles. The second are usually ineffective because there is no inflammation."

* Limited physical activity: Don't bend, don't lift, don't run. "Nonsense," says Sarno.

Other myths about back problems, according to Sarno:

* "Man wasn't meant to walk upright." Sarno says "Ridiculous. Man has had some 3 million years to adapt."

* Diagnosis of "strained or weak muscles." They're not sources of back pain, says Sarno. "Witness the large number of superbly trained young athletes with back problems, no identifiable disc 'disease' and no weak muscles."

Other fallacious prohibitions: High heels, swimming the crawl--anything, in fact, says Sarno, that suggests that the back is fragile.

Although each year Americans undergo some 200,000 operations--called laminectomies--for herniated discs, there are no reliable statistics on success rates, says Sarno. If the pain returns, even if it is in exactly the same place, the surgeon will say something like, "Oh it must be another disc . . ."

Conventional back specialists are at a loss to explain why many people have extremely advanced "disc disease" and bone spurs, yet suffer no pain, and some people have excruciating pain with only minor "abnormalities."

Sarno believes it is because the pain is not caused by the discs. Changes in discs and the growth of bone spurs are normal and essentially benign signals of aging--like graying hair.