The scientists who study the gene -- the unit that determines all heredity and body structures -- have discovered a startling new clue to the way human and animal genes work.

The words "startling" and "exciting" and "important" were used by Dr. Ronald Brown of the Carnegie Institution of Washington yesterday as he told of the new advance.

He and colleagues discovered that the controlling section of a key gene in the frog -- a gene found in may animals, including humans -- is unexpectedly a section in the middle, not at the ends, of the gene.

Within 10 years, Brown predicted, discoveries like this deceptively simple-sounding one, and the way these discoveries are being made, will lead to new ways to attack some of our greatest genetic problems, such as genetic diseases or crop yields.

"If I were courageous, I'd say within five years," he said.

"We are beginning, our group and others, a new kind of genetics" to learn how animals and human genes work, he said.

Until now, almost all knowledge of the ways genes work, almost all the discoveries of the new biological revolution, have been based on studies of the genes of bacteria and viruses, he said.

In all living things -- in bacteria, viruses, animals, humans -- genes are simply individual segments, strings of DNA (deoxyribonucleic acid), on DNA molecules, long, winding spiral assemblies.

The living organisms examined most closely, because they have been easiest to study, have been bacteria and viruses. They are simple. They multiply quickly. And in particular, the bacteria E. coli (which inhibit the human gut) and a virus called a bacteriophage (because it attacks bacteria) have been the most studied.

In recent years, however, Brown's group at the Carnegie embryology laboratories in Baltimore turned to another creature: the frog. More exactly, they turned to Xenopus, often called the African clawed toad.

More exactly still, Brown said, Xenopus is neither a frog nor a toad, but a relative of both. But he most often called it a frog.

Using new methods developed by other biologists, Brown, Daniel Bogenhagen and Shigeru Sakonju first isolated and learned the structure of the "5S" Xenopus gene. This gene dictates the manufacture of a chemical called RNA (for ribonucleic acid). This RNA becomes a part of the ribosomes, which are cell's assembly points for manufacture of proteins, the main building blocks of all body structures.

The Carnegie scientists then grew the 5S gene in bacteria, duplicating or cloning it by the billions by new recombinant methods. Then, in new techniques they have devised, they made their clones function like the frogs' own in an extract made from frog egg cells.

"So what we have," Brown said, "is not only a new piece of knowledge but a new way of doing genetics.

"In what we know about this gene now, and the way that it functions, we have only the first step in a puzzle. But the answer, when we get it, will begin telling us how animal and plant genes are controlled."

All animal and plant genes are almost certainly not controlled in just the same way, he emphasized. But, "The thing we're excited about is that we now know how to study how this animal gene works, and the same method will help tell us learn how many genes work," he said.

A Carnegie announcement yesterday added, "Developmental biologists seek to understand how an egg cell differentiates [and] becomes a whole organism . . . How is one cell regulated to manufacture skin protein and another to make blood? . . . How do individual genes know when to turn on and off?"

What does this mean?

'Well, I can't tell you what disease doctors someday will cure. But I can say that I believe knowledge will lead to cures," Brown concluded.