PEDIATRICIAN Dr. Lendon Smith has become a television personality because he injects a lot of humor into his advocacy of nutritional and megavitamin therapy for everything from dandruff and backache to hyperactivity and anxiety. But Dr. Smith was not laughing in 1973 when the Oregon Board of Medical Examiners revoked his privilege to prescribe addictive drugs.

Smith, author of the best seller "Feed Your Kids Right," which brought $600,000 for paperback rights, says he is no longer "embarrassed" about his probation in the State of Oregon. "I can handle it. I've gotten over my feelings of anger. It was a bad time in my life."

Smith began his career like most other pediatricians, curing rather than trying to prevent illness. Now he believes that "most illness is the result of improper nourishment." His book divides children into five levels, from the healthiest (fun-to-have-around child. A joy), Level 1, to the extremely retarded or malformed, bedridden or terminally ill, Level 5. According to Smith's theory to make children in levels 2 and 3 like children in Level 1 "only diet changes" are needed. Children in levels 4 and 5" would more likely need high potency vitamins, even injections of high doses, to reverse rapid slippage."

In today's scientific lingo, children in levels 3 and 4 might also be described as hyperactive.

Smith admits that the loss of his right to prescribe most addictive drugs, including the one commonly prescribed for hyperactive children, "was an incentive" to start treating these children with nutritional therapy. But he said in a telephone interview last week, "I was already getting interested in it."

Others in Portland, where Smith lives and practiced, say he "believed in prescription writing until he could no longer write prescriptions and then he had to come up with another way of doing what he was doing."

Until the Oregon Board of Medical Examiners restricted him, Smith, like many pediatricians, prescribed Ritalin to calm hyperactive children. Those are children who are restless, unable to concentrate or sit still, who exhibit wild swings in moods.

After working in a free clinic for drug addicts Smith theorized that many heroin addicts had been hyperactive children and he prescribed Ritalin for them. "I figured I was familiar with Ritalin and I could help some of these people, but it was more than I could handle. It got out of hand. It was pretty naive of me to think I could do it."

What happened was that the heroin addicts, some of whom were on methadone, took Smith prescriptions and sold them in order to buy heroin.

According to Joseph Ulwelling, executive secretary of the Oregon Board of Medical Examiners, Smith "was brought before the board and talked to before his license was revoked. It's against the law to maintain someone on drugs if they are drug addicts unless you have federal approval to run a program. But at any rate," Ulwelling said, "Ritalin is not approved for heroin addicts."

Ulwelling says that Smith is "a good physician -- bright, articulate, very responsive," but he "may have run into an ego thing of 'I know best.' He's one of those people," Ulwelling said, "who's always right. But a physician is usually always outmaneuvered by an addict who is trying to get medicine."

A few months after Smith was put on probation, he asked the medical board to allow him to write prescriptions for addictive drugs once again. On Jan. 14, 1974, the board agreed, under certain conditions that included weekly reports and a promise to limit his practice to children. But on April 10, 1975, Smith's license to write prescriptions for those drugs was once again lifted because the board felt he was writing too many for Ritalin. "They did not believe there were that many hyperactive children," Smith said. Four months later the suspension was modified, permitting Smith to write prescriptions for one category of controlled drugs -- the least addicting Ritalin was not included.

Since that time the terms of Smith's probation have been modified slightly.

Instead of appearing before the board four times a year, he need only appear once.

Smith's reputation in Portland is mixed. A former colleague at the free clinic, Dr. Charles Spray, the only physician who would permit his name to be used, says Smith is a "fine man. I think he was just honestly misguided and probably got in over his head. He was, and is, in an area that is all gray. There are no standard programs for treatment." Spray says the state's board of examiners is very strict.

The establishment medical community resents Smith's flamboyant style, his many television appearances, including several on the Johnny Carson's "Tonight" show. They consider the kind of medicine he practices "fringy." "He doesn't do this for profit," said one colleague, who believes Smith likes to have his name in the headlines. Said another doctor: "I think he is a very honest man, nothing crooked. It's just that he doesn't go through regular channels. Dunny has had one fad after another. I think he's honest in his attempt but not scientific. In private practice you cannot have double blind studies."

(That's a reference to the scientific method for determining whether or not a course of treatment works. One group receives the medication; the other receives a placebo. Neither subjects nor researchers know which group is which.)

Smith acknowledges that double blind studies would be useful in proving that nutritional therapy controls hyperactive behavior, but he says there's no way to do them. "I think anecdotal evidence is where we have to start. We're just accumulating evidence." His evidence indicates that if you remove "junk" food from your hyperactive child's diet (all forms of sugar, white flour, most processed foods, even pasteurized milk for a month) and give the child megadoses of vitamins and minerals, the hyperactive behavior will disappear. (Curiously, Smith recommends substituting raw honey for sugar and of nine sweet recipes given in his book, six use honey.) Asked if the improved behavior of the children might be due to a placebo affect, Smith said, "I don't know how to answer that."

Few traditional physicians accept the thesis that diet can affect behavior, though some have been willing to try the Feingold diet for hyperactive patients. That diet removes artificial colors and flavors from the diet and foods which contain a naturally occuring substance called salicylates.

Even fewer physicians believes that megadoses of vitamins and minerals will help. In addition there is some concern about the dangers from the large amounts of vitamins A and D which Smith recommends. Smith acknowledges that huge amounts of vitamins A and D can be toxic, but he says, "I carefully pointed that out in the book. There are certain symptoms you have to watch out for."

In its review of his book, the newsletter Environmental Nutrition said: "The author's latest work . . . is a mishmash of inaccuracies and recommendations for megadoes of nutrients to cure everything that ails the modern child.

"Perhaps the advice which is most alarming in its glibness is Dr. Smith's promise that 'a few teaspoonsful of brewer's yeast in a baby's diet each day can change a thin, weak, pale irritable infant into a smiling pink-cheeked, hungry, active, fun-to-show-off-to-relatives baby.' A child of this description is sick and needs prompt medical attention, not a trip to the health food store. The author rarely cautions parents to consult their pediatrician first before trying his remedies even though, few, if any, have research to back them up.

"The real problem with the regimen, however, is its finale -- huge doses of vitamins and minerals. . ." The reviewer, registered dietitian Betty Ivie Goldblatt, explained in an interview that "taking excessive doses throws off the inherent balance of all nutrients working together. Excessive Vitamin A can cause damage to the liver; excessive Vitamin D can retard growth."

In one place Smith says 15,000 to 30,000 units of Vitamin A "is about right for most of us . . . increased amounts of 50,000 to 150,000 units would be needed if there is constant eye use or strain, psoriasis, warts, eczema, gum disease or alcoholism." He says nothing about toxicity until many pages later. The Recommended Daily Allowances of Vitamin A is 5,000 units. In another place he recommends 5,000 to 10,000 units of Vitamin A. In a third place he says the 30,000 to 50,000 units of Vitamin A are part of his stress formula. Smith recommends 400 to 1,500 units of Vitamin D (400 is the RDA) and does warn that it can be toxic. Smith suggests these large amounts of vitamins for limited periods of time, advising the reader "to find his own specific requirement."

Smith admits there is a tendency among many people to believe that if a little is good a lot is better. "I worry about those people," Smith said, "but I think people have to figure this out for themselves."

Nor will readers of his books find any reference to Smith's 10-year medical probation. "No matter how I would have handled it, it would have looked as if I were appealing for sympathy. Some people might say 'Oh, that's disgusting.' Others might say, 'Oh, that makes sense so maybe it would have been a good thing to get it in there."

Smith has just sent the manuscript for a new book off to his publisher and has decided against chronicling the event which he says "was an incentive" for his current treatment of hyperactive behavior.