WASHINGTON (AP) _ Genetically identical monkeys are being cloned by Oregon researchers, who are splitting early-stage embryos and then implanting the pieces into mother animals.

The technique has so far produced only one living rhesus monkey, a female named Tetra, but Professor Gerald Schatten said four more animals are on the way.

Schatten, a researcher at the Oregon Health Sciences University in Portland, said the goal is to produce identical monkeys that could be used to perfect new therapies for human disease.

The study will appear Friday in the journal Science.

Most medical therapies are now first tested in mice, but monkeys are much closer to human biology and would be more reliable in developing daring new techniques such as gene therapy or growing new organs using stem cells, said Schatten.

``It is a huge leap from a mouse to a patient,'' said Schatten. ``The monkeys could fill that scientific gap.''

In their research, Schatten and his colleagues created monkey embryos in the laboratory by combining sperm and egg. When the embryos grew to an eight-cell stage, they were each split into four parts, with each part containing two cells. These were then nurtured into new embryos.

In effect, he said, the single embryo became four embryos, all genetically identical. The new embryos were then implanted into the uteri of different mothers.

In the first test of the technique, the researchers produced Tetra. A twin to Tetra was implanted, but miscarried.

Now, said Schatten, four mother monkeys are pregnant with cells taken from two separate embryos. Three of the mothers were implanted with two unrelated embryo splits and the fourth mother was impregnated with a single embryo split.

Schatten said it will not be known until May, when the animals are born, which of the split embryos are developing into infants.

``It is possible that we will have genetically identical monkeys born to different mothers,'' he said.

The technique is not cloning in the sense of producing a genetic duplicate of an adult, such as was accomplished with the famed Scottish ewe named Dolly.

Instead, said Schatten, the technique clones genetically identical infants that arose from the same embryo. It is virtually unknown, he said, for identical twin rhesus monkeys to be produced naturally.