It sounds like mechanized witchcraft: hooking up a Rube Goldberg-looking contraption to a twisted or stunted limb to make it grow to normal length and shape. That it originated in deepest, darkest Siberia doesn't make it any more believable.

But according to American orthopedic surgeons who have been there to learn how it's done, and patients treated in the West, the Ilizarov technique for repairing bones really works. In fact, says one such surgeon, Dr. Dror Paley of the University of Maryland School of Medicine, who has used the method on 70 patients, "it often works when other methods cannot even be attempted or have already failed."

As for Ilizarov -- 67-year-old Dr. Gavril Abramovitch Ilizarov -- he has practiced orthopedic surgery in Kurgan, a provincial industrial city 1,050 miles due east of Moscow, for more than a third of a century.

Now head of a 1,000-bed institute and 10 affiliated centers entirely devoted to his therapy, Ilizarov's road to success was difficult. He became the object of the Russian medical establishment's suspicion when -- in 1951, at a small, poorly equipped hospital for war casualties -- he began to treat difficult fractures with an operation and an apparatus of his own devising.

Soon he was not only putting badly shattered bones back together but also lengthening them and repairing damage to limbs done by birth defects, bone cancer surgery, deep-seated bone infections and diseases like polio.

Yet so hostile and disbelieving were his critics that he and the method might still be languishing in obscurity had Soviet athlete Valery Brumel -- then world champion high jumper -- not been seriously injured in a Moscow motorcycle accident in 1967.

"Brumel got the best conventional treatment there was in Russia," recalls Dr. Vladimir Golyakhovsky, who was an orthopedic surgeon in Moscow at the time and now, having emigrated, is at the Hospital for Joint Diseases Orthopaedic Institute in New York. "But nothing worked very well, and it looked as if his right leg would be permanently crippled.

"On my advice -- I had been there, so I knew -- Brumel went to Kurgan, where Ilizarov repaired the leg. A year later, he could again clear 2 meters {6 feet, 7 inches}, and Ilizarov, despite his critics, became as famous in Russia as Brumel himself." The Ilizarov technique for extending bones takes advantage of bone's natural ability to repair itself. Key to its success is a delicate -- and virtually bloodless -- operation that must be performed before the mechanical device is installed.

Through tiny incisions in the skin, the surgeon cuts the bone -- but not all the way through. The marrow is spared, because its blood vessels provide the nourishment for the generation of new bone. It is somewhat like cutting into the bark of a tree without damaging anything underneath.

Then thin wires are run criss-cross through the bone above and below where it has been cut and are pulled through the muscles and skin. They are attached, under tension, to metal rings that circle the limb.

The rings are connected to each other with threaded tie rods. All in all, the apparatus looks very much like something built from a child's Erector set.

Beginning a few days after surgery, patients begin to turn knobs on the tie rods four times a day to tighten them slightly. In turnbuckle fashion, each turn pulls the cut ends of the bone apart by about 0.01 inch. The bone responds by continually filling in the gap. The tension causes the nerves, skin and muscles to keep pace.

"The whole idea here is to mechanically exploit the natural behavior of bone to make it grow just as it would in a normal fetus or child," says Paley, a Canadian, who has translated more than 100 of Ilizarov's scientific papers into English and is the North American surgeon most experienced in the technique. "And no bone grafts are needed as they are with other bone elongation methods, which is a great advantage in itself. For one thing, patients often need only one operation, rather than the usual three or more. And for another, there are far fewer infections and other complications."

Just how long the patient wears the frame depends on the extent of correction required. Typically, it takes a month for a centimeter (0.4 inch) of new bone to form and harden. Thus, if a limb is four inches too short, the frame is left in place for about 10 months.

Sometimes treatment time can be halved by cutting a too-short bone at two levels instead of one, requiring a frame with two sets of wires and external parts.

In either case, instead of spending weeks or months in the hospital, as frequently is the case with other limb-lengthening and repair methods, Ilizarov patients are usually disharged in seven to 10 days, returning as outpatients for x-rays, fine-tuning of the apparatus and physical therapy.

Many patients go back to school or work while wearing their frames. In fact, they are instructed to be active because frequent weight-bearing exercise is crucial to success of the therapy. Just why is not known, but lack of weight-bearing has been shown to cause deterioration of bones in astronauts subjected to zero gravity and people long confined to bed.

During therapy, young children seem to have little pain. But teen-agers and adults are not always as lucky. Although turning the knobs usually doesn't hurt, says Paley, the constant tension that their muscles are under tends to make them ache, particularly at night.

Few American doctors have yet tried the Ilizarov system, but many are watching its use with great interest. Says Dr. Charles Clark, an orthopedist at the University of Iowa Hospitals in Iowa City: "I haven't used the system myself, but my understanding of it is that it is a promising and exciting approach." Before coming to the University of Maryland in late 1987, Paley was at the Hospital for Sick Children in Toronto. There, one of his Ilizarov patients was Jane Boyce, who, at 14, was only 4-foot-4. Because she is a hypochondroplastic dwarf -- a genetic condition -- she would ordinarily have stayed that height for the rest of her life.

Last June, Paley operated on one of her upper legs and the opposite lower leg, and this June another surgeon will operate on the remaining upper and lower limbs to complete the lengthening process.

After seven months of being in frames (they were recently removed), the Hamilton, Ontario, teen-ager's legs have grown 4.7 inches and a year from now they are expected to be 2.4 inches longer still, giving her a final height of 4-foot-11 -- short to be sure, but within normal range.

The treatment is also straightening her bowed legs. "She had reached an age where she was very self-conscious about her height and other youngsters had teased her about being so short," says her mother, Janet Boyce.

Jane is delighted but says that the seven months she has already spent in treatment were "very hard to go through" and that she expects the second round of therapy to also be arduous.

Even at that, hers is a relatively simple case. Many dwarfs have badly swayed backs and arms, as well as legs, that are very short. Such problems also can be tackled with the Ilizarov system, and not only in dwarfs.

Just as bone can be lengthened the Ilizarov way -- by 10 inches or more -- it can also be widened, straightened, shortened or realigned because the circular rings can be assembled in many combinations and configurations. Even amputation stumps can be enlongated.

Amputation stumps -- for example, legs amputated above the knee -- do not develop new joints when lengthened. Nonetheless, lengthening them can be worthwhile because an elongated stump can more easily be fitted with a prosthesis.

Perhaps the most dramatic use of the technique is in treating severe congenital bone malformations. Dr. Stuart A. Green of the Rancho Los Amigos Hospital in Downey, Calif., is another of the American orthopedists who has been to Kurgan and now is teaching the Ilizarov system to other orthopedists here, as well as using it himself.

"There are certain kinds of birth defects for which early amputation has been the standard treatment in the United States," says Green. "Typically, for example, such a baby has one leg far shorter than the other below the knee and the foot on that leg is badly twisted. Often the foot is also missing the two outer toes.

"Or, it may be that the child has a malformed hip and a thigh bone so small that the leg looks like a little sausage between the hip and the knee. In cases like that, the usual treatment, while not amputation, is just as drastic. Orthopedic surgeons push the thigh bone up and fuse it to the hip and then turn the foot and ankle around backwards so that they can be used as the knee for an artificial leg.

"You can imagine how upset parents are when they are advised to have this done or told that amputation is the best thing for their child," Green said. "Well, the professor takes one long careful look at such cases and says 'I can fix that; I can operate to make that leg normal or nearly normal.' And, having now performed more than 500,000 of his procedures, he can. All of us who have been to Kurgan have seen that for ourselves."

On a visit to California last year, Ilizarov advised the American parents whose badly handicapped children he examined not to rush them into irreversible surgical procedures and instead to wait until treatment by his method is more widely available here.

Green does not himself treat such children. But Paley and Dr. Victor H. Frankel (who has also been to Kurgan) and his colleagues at New York City's Hospital for Joint Diseases Orthopaedic Institute are planning to treat some youngsters with the complex problems Green describes.

Indeed, all three U.S. orthopedic surgeons have already used the Ilizarov system to treat a variety of somewhat simpler bone abnormalities. The first patients Green and Frankel treated, for example, were adult accident victims who "had nothing to lose," because they otherwise would have had to have a leg taken off.

One of Paley's patients was a 14-year-old boy whose crippled and twisted left forearm was restored to normal dimensions and a full range of motion. Another patient was a 10-year-old boy who -- despite five earlier operations for a club foot -- could not walk without hopping on the foot, until the Russian therapy added 1 1/2 inches to its length.

Can patients of any age benefit from this surgery? Between about 5 and 60, the answer is usually yes. Children must be mature enough to cooperate in their treatment, and, after about age 60, limb elongations cannot be expected to succeed.

Above 60, however, the Ilizarov method can still be used for other purposes such as mending fractures that have failed to heal. Two further questions about this technique are often asked: First, can the Ilizarov device be used for complicated fractures in an emergency room? And second, what about using it for normal people (would-be basketball players, for instance) who simply want to be taller than nature decreed?

Answer No. 1 is that, although Ilizarov can operate and fit a frame in about 20 minutes, U.S. orthopedic surgeons can't; at least not yet. While they do not rule out the possibility of using it more routinely eventually, they say it would be impractical to try to do so now.

Besides, Richards Medical Co. of Memphis, U.S. distributor of Ilizarov equipment, has made arrangements with the Food and Drug Administration to limit sale of the apparatus to specialists who undergo approved training in its use.

As for the second question, Ilizarov is said to have treated several dancers from the Bolshoi Ballet who wanted longer legs. But he is also said to now regard this as "irresponsible" -- a view that Paley, Green and Frankel share.

One of Paley's patients, in fact, is a 40-year-old man with legs of unequal length who recently asked him whether, besides elongating the shorter leg, he couldn't make him four inches taller. "I could," Paley told the man, "but I won't."

TECHNIQUE MORE COMMON IN EUROPE

Although new to North America, the Ilizarov technique was introduced in the early 1980s into Western Europe, where about 100,000 of these procedures have been done in Spain, France and Italy. One Italian orthopedist -- Dr. Giovanni De Bastiani of the University of Verona -- operates in the same way as Ilizarov does but has developed a frame that is less bulky than the Soviet frame and is easier for the surgeon to assemble and apply.

Dr. Charles T. Price of the Orlando Regional Medical Center in Orlando, Fla., is using the Italian frame, which, instead of the Ilizarov frame's multiple circular and longitudinal elements consists of fewer parts, all of them straight.

Price reports "excellent results" in lengthening the legs of both adults and children with the Italian frame, which he likes for its simplicity. But he notes that it cannot tackle bone problems as complex as the Ilizarov frame can. Also, with the Italian frame the patient cannot put full weight on the limb.

Judith Randal is a Washington science writer.