Swiss and Finnish genetic engineers have learned to make a close copy of one of the human body's scarcest, most important substances -- a natural disease-fighting, cancer-fighting compound called interferno -- they said yesterday.

The scientists have induced extracts of human genes to duplicate the human interfron gene in laboratory bacteria, thus turning the bacteria into factories to make a substance very close in nature to human interfron.

These bacterial factories, the scientist said, should soon begin to produce the first substantial quantities of an interferon-like substance. And, in the words yesterday of Dr. Walter Gilbert of Harvard University, one of the world's leading molecular biologists, the new substance might "knock out" some important virus diseases, as well as attacking cancer.

The new work was done partly at the Finnish Red Cross Center in Helsinki and partly at the University of Zurich by scientists working on behalf of Biogen SA, a small, largely European firm in the new business of combining DNA or genetic materials to try to make commercial products.

The work was announced in Boston by Dr. Charles Weissmann of the University of Zurich; Robert Cawthorn, the firm's president; and Gilbert, a Harvard biologist who heads Biogen's scientific advisory board.

Biogen is partly owned by International Nickel Co. (Inco) of Toronoto and in smaller part by Schering-Plough, a major American pharmaceutical firm. A Schering by Schering-Plough, a major American pharmaceutical firm. A Schering-Plough official arranged the Boston news conference.

Interfron is a compound released by some of the body's cells when they are attacked by viruses, toxic chemicals or other enemies, including cancer. It is being tried with such promising results against such a wide variety of human virus infections, and several kins of cancer, that many scientists believe that it may prove to be almost a "universal drug," much like penicillin.

Based on optimistic though early reports in treatment of some kinds of cancer, the government's National Cancer Institute is about to spend between $4 million and $10 million to make enough intereron by cumbersome present methods to treat 400 cancer patients.

The Biogen scientists are still making interferon only in speck-like quantities. Buty they are confident, Weissmann said, that they can increase the yield.

Gilbert called the work very much like the early development of antibiotics in its potential.

"It's a very important discovery" if it bears out its promise, Dr. Frank Rauscher, senior vice president of the American Cancer Society and former National Cancer Institute director, said in New York.

Still, Rauscher said, the substance must be purified and prove non-toxic, then must prove to be as effective as natural interferon.

Interferon has been known to scientists fokr nearly 25 years.

Only recently, however, has enough been extracted to try in even small groups of patients.

Most of the current supply is made by the Finnish Red Cross by isolating it from human white blood cells.

There are two other equally slow manufacturing methods, both involving collecting interferon from human cells grown in laboratory cultures.

But the chemical's current price -- in the neighborhood of $10,000 to $15,000 for enough to treat one patient -- has made large-scale studies almost prohibitively expensive.

Just the same, the drug has been tried with promising results in small numbers of patients with hepatitis; genital herpes (a common venereal disease), chicken pox, respiratory infections and the grim cytomegalovirus infection of the brain.

Last March, the American Cancer Society started the largest test of interferon so far, a $10.4 million trial in 150 to 200 patients at 10 cancer centers. Very preliminary results have shown at least some activity, and often high activity, against some breat cancers, osteogenic sancomas, malignant melanomas and lymphomas.

Whether interferon will actually cure cancer or other diseases still must be proved. But other scientists too are trying to duplicate natural interferon, and many believe that before the 1980s are ended science will have a new class of drugs.