WASHINGTON (AP) _ Scientists have genetically engineered a type of rice that could end vitamin A deficiency in the developing world, a problem that is a common cause of blindness and other health problems in millions of children.

The researchers at a Swiss laboratory spliced three genes into the rice to make it rich in beta carotene, the source of vitamin A, according to a report on their findings appearing Friday in Science magazine.

The new crop, dubbed ``golden rice'' because of the hue the beta carotene gives it, is not expected to be available to farmers for several years. Also, scientists still have to determine if the altered rice loses any of the original rice's nutritional value.

Nonetheless, the International Rice Research Institute already is working on breeding the new trait into popular varieties.

A U.S. biologist, in a Science commentary on the findings, hailed the research as a ``technical tour de force'' because of its complexity and said it ``exemplifies the best that agricultural biotechnology has to offer.''

The Rockefeller Foundation, the lead sponsor of the rice research, views biotechnology as a solution to world hunger, and also wants to develop crops that would be resistant to drought, pests and soil toxins. Scientists believe it eventually will be possible to put iron and other nutrients in plants once the genetic pathways are known.

Rice is a relatively poor source of many essential nutrients, including vitamin A, but is the staple for half the world. An estimated 124 million children worldwide are deficient in vitamin A, including a quarter million in Southeast Asia who go blind each year because of the problem. Improved nutrition could prevent 1 million to 2 million deaths a year, scientists say.

Rice naturally produces its own beta carotene, but it is lost in the milling process. The biotech variety would have the beta carotene right in the endosperm, the part people eat.

The rice is unlikely to be sold in the United States or Europe, but it has public relations value for proponents of biotechnology.

Most biotech crops developed so far are either tolerant of herbicides or toxic to insects, traits of little benefit to consumers, and the seed companies are struggling to overcome consumer resistance in Europe and Asia.

The biotech rice could improve the industry's image because it was developed without commercial funding and will be easily available to farmers, said Mary Lou Guerinot, the Dartmouth College biologist who wrote the Science commentary.

``One can only hope that this application of plant genetic engineering to ameliorate human misery without regard to short-term profit will restore this technology to political acceptability,'' she wrote.

Critics of biotech crops say not enough is known about their safety or effect on the environment. While acknowledging the potential benefit of the rice, they say that should not be used to block efforts to require stricter regulation.

``I certainly agree that certain applications of biotechnology can have great social value, but that in no way obviates other concerns,'' said Rebecca Goldburg, senior scientist for the Environmental Defense Fund.

It will take more testing to determine whether the biotech rice will meet a person's daily needs for vitamin A. Although the laboratory rice may have sufficient beta carotene, levels could vary in the varieties that are bred from it, Guerinot said.

Getting consumers to accept the yellowish rice also could be a challenge. They will have to be convinced the rice will prevent blindness and other health problems, said Per Pinstrup-Andersen, director general of the International Food Policy Research Institute.

``You're changing the color of a very basic food staple for millions of people, and that's never easy. But I think it can be done,'' he said.