UPDATE 1-Clones' offspring may be in US food supply - govt

(Adds companies not using cloned animals, USDA comments)

WASHINGTON, Sept 2 (Reuters) - Food and milk from the offspring of cloned animals may already have entered the U.S. food supply, the Food and Drug Administration said on Tuesday, but it would be impossible to know because there is no difference between cloned and conventional products.

The FDA said in January meat and milk from cloned cattle, swine and goats and their offspring were as safe to eat as products obtained from traditional animals. Before then, farmers and ranchers had followed a voluntary moratorium that prevented the sale of clones and their offspring.

“It is theoretically possible” offspring from clones are in the food supply, said Siobhan DeLancey, an FDA spokeswoman.

Proponents, including the Biotechnology Industry Organization, say cloned animals are safe and a way to create animals that produce more milk and better meat and are more disease-resistant. There are currently an estimated 600 cloned animals in the United States.

The small cloning industry and the FDA have maintained cloned animals and their offspring are as safe as their regular counterparts. Cloning animals involves taking the nuclei of cells from adults and fusing them into egg cells that are implanted into a surrogate mother.

FDA and the U.S. Agriculture Department have said it is impossible to differentiate between cloned animals, their offspring and conventionally bred animals, making it difficult to know if offspring are in the food supply.

“But they would be a very limited number because of the very few number of clones that are out there and relatively few of those clones are at an age where they would be parenting,” said Bruce Knight, USDA’s undersecretary for marketing and regulatory programs.

Even as the FDA unveiled its final rule, USDA asked in January for the cloning industry to prolong the ban on selling products from cloned animals during a “transition” period expected to last at least several months. That ban did not extend to meat and milk from the clone’s offspring.

Critics still contend not enough is known about the technology to ensure it is safe, and they also say the FDA needs to address concerns over animal cruelty and ethical issues.

“It worries me that this technology is out of control in so many ways,” said Charles Margulis, a spokesman with the Center for Environmental Health. The possibility of offspring being in the food supply “is just another element of that,” he said.

Despite the backing from FDA, major food companies including Tyson Foods Inc TSN.N, the largest U.S. meat company, and Smithfield Foods Inc SFD.N have said they would avoid using cloned animals because of safety concerns.

The list grew on Tuesday after the Center for Food Safety and Friends of the Earth said 20 food producers and retailers vowed not to use ingredients from cloned animals in their products.

The list, provided by the two groups, included Kraft Foods Inc KFT.N, General Mills Inc GIS.N, Campbell Soup Co CPB.N, Nestle SA NESN.VX, California Pizza Kitchen Inc CPKI.O and Supervalu Inc SVU.N.

In a letter to the Center for Food Safety, Susan Davison, director of corporate affairs with Kraft, said product safety was “not the only factor” the company considers.

“We must also carefully consider additional factors such as consumer benefits and acceptance ... and research in the U.S. indicates that consumers are currently not receptive to ingredients from cloned animals,” she said. (Editing by Christian Wiessner)