Cloning: science in search of an ethic

Gregory Farrand shepherds ''cow 6103,'' a cross between a Simmental and Hereford, into a holding cage at a Colorado State University research facility in Fort Collins.

His purpose: to ''flush'' a week-old embryo harmlessly from its mother - so that the tiny cell cluster can be split in two under a microscope to produce a set of ''cloned'' twin calves.

Welcome to the new age of cattle breeding. No sounds of thundering hoofs here. No swirls of dust being kicked up. No kerchiefed cowboys.

Here, lab-coated scientists toil in a complex world of microscopic embryos and large expectations of producing superior strains of animals.

The science of cloning and related embryo-engineering technologies, not long ago considered science fiction, are slowly revolutionizing animal breeding on the farm. In the next decade, they promise to produce livestock that are more disease-resistant, eat less food, and produce more beef and milk.

At the same time, however, the new technologies are tumbling out of the labs fast enough to raise troubling social questions.

At present, embryo engineering is an unregulated practice. But the possibility of applying these techniques to humans continues to make some academic and religious leaders uneasy - since the idea of human cloning strikes at the fundamental issue of individual identity.

Cattle cloning is an outgrowth of earlier work in the area of embryo transfer. Embryos were first successfully ''harvested'' from rabbits in a British lab 93 years ago. Cattle breeders have been doing it commercially for more than a decade.

Currently, some 50 firms are involved in the embryo-tranfer business in North America. An estimated 40,000 calves will be born from transplanted embryos in the United States this year - double the number of five years ago, but less than 1 percent of all cattle.

Yet the technologies, researchers say, hold promise far beyond the numbers. While a prize cow (for instance, one with superior milk-producing traits) can normally bear only one calf a year, embryo transfer can boost that number to as many as 100. And with the recent advent of embryo splitting, or cloning, the number of births can be dramatically increased beyond that.

The splitting of cattle embryos, pioneered in England, was first carried out in the US by researchers at Colorado State University. They delivered a set of identical twins in May of last year. Since then several dozen other ''cloned'' twin calves have been produced there and on farms across the country.

Scientists are now working on splitting embryos in four or more parts. ''It will get to the point where you will almost be able to get as many calves as you want,'' predicts George Seidel, an associate professor in Colorado State's department of physiology and biophysics.

So far, the process is expensive: $2,000 or more per calf. One factor reducing the cost, however, is the ability to freeze and store embryos. This allows breeders to choose when and where they want calves to be born.

Freezing also permits the rapidly growing business of exporting embryos. Frozen embryos are now being shipped to Europe, Asia, and Africa. ''The export business is going to be enormous in the future,'' says Dr. Stanley Leibo, a scientist at Rio Vista International Inc., a San Antonio, Texas, embryo-transfer firm.

In a related development, Genetic Engineering Inc., a Colorado firm, claims to have pioneered a reliable method of predicting the gender of unborn cattle. For ranchers this would be a boon: It means dairy farmers would be able to weed out unwanted bulls, while beef herders could screen out milk-producing cows.

Underlying all this, questions linger. How far should or might embryo engineering go? Even the seemingly innocuous practice of determining and selecting the sex of calves before birth, if carried far enough, raises the possibility of altering the makeup of entire populations - not only of animals, but also of humans.

Cloning - regularly done by gardeners who start plants from cuttings - appears to have entered a new phase. The next logical step bears close watching.