Scientists have discovered that certain animal and human cancers may share a "closely related" gene thought to be "instrumental" in transforming a healthy cell into a cancerous one.

Dr. Robert A. Weinberg, a researcher at the Massachusetts Institute of Technology, said today that this suggests there may be a small number of "target" genes common to both animals and humans that are key elements in the complex triggering of the cancer process.

They are called target genes because they are susceptible to conversion to cancer genes--and capable of making normal cells cancerous--through influence by outside factors such as radiation and chemicals.

But the 39-year-old biologist cautioned that the basic research may not have practical human payoffs for five to 10 years. He does consider it a "big step forward" in understanding how a normal cell is converted into a tumor cell.

The latest findings follow the isolation last fall for the first time of "oncogenes"--or cancer genes--in several forms of human cancer using genetic engineering techniques. This follows earlier research indicating that genetic material from cancer cells when introduced into normal mouse cells may transform them into malignant ones.

It also appears to vindicate, said several researchers here, the years of investment in cancer virus research in animals, which makes that large body of information more valid and therefore valuable to researchers.

Weinberg said that so far similar genes have been found in both human bladder cancer cells and a rat tumor virus called Harvey sarcoma. His research team originally obtained the animal tumor virus from the National Cancer Institute's Dr. Edward Scolnick and "stumbled across" the match with a human counterpart only about a month ago.

About two weeks ago, Weinberg traveled to Scolnick's laboratory in Bethesda, carrying a bottle of champagne to celebrate the occasion. He also presented the results in a private seminar with NCI officials.

At the time, another NCI researcher, Dr. Mariano Barbacid, indicated that he too had found a similar link between a mouse tumor virus and human bladder cancer. Scientists said they understood there was a similar finding at Boston's Sidney Farber Cancer Institute.

Weinberg emphasized that his research does not suggest any role for viruses in causing the "great majority" of human cancers. Instead, it suggests that similar cancer genes in animals and humans may be activated by several different routes, but the way they function after being turned on may be the same.

The findings to date suggest that only a small number of genes--about a dozen of the 50,000 in a normal cell--may be the targets of chemicals, radiation or other cancer triggers in humans, while a corresponding group of genes may be vulnerable in animals to viruses and other agents that transform them to a cancerous state.

"The animal tumor viruses," which have been well studied over the past decade, "may now give us insight into how the human cancer genes function," said Weinberg.

The limited number of cancer-causing genes catalogued to date may well be repeated in the 100 or so different forms of the disease in humans, he said. Because each gene produces a characteristic protein, it eventually may be possible to develop tests to detect the cancers at early stages.

National Cancer Institute associate director Peter Fischinger called it "very exciting," adding that it appeared that similar linkage between animal and human genes had independently been made by at least two other teams.

American Cancer Society President Dr. Robert Hutter said the findings represented "one of the most profound" advances in "fundamental" cancer research.

None of the discoveries, which only occurred in recent weeks, have yet been published. Weinberg, however, confirmed his laboratory's success to reporters at a cancer seminar here after a report leaked from a closed scientific meeting that ended Sunday in California.

NCI researcher Dr. Robert Gallo, who has found that viruses may play a role in some rare forms of cancer, said here that he and others at laboratories around the country also will be attempting to cross-match human and animal cancer genes.