The science of cloning is moving so rapidly, according to experts, that the ethical debate surrounding the procedures is about to be left in the dust. Full-scale human cloning is no longer a question of if, but when.

Yesterday, researchers at a South Korean hospital claimed they had combined an egg and a cell from a single donor to produce the first stages of a human embryo. The four-cell embryo, which theoretically could have grown into an identical replica of the woman donor, was not implanted in a woman and the experiment was halted.

Here is a chronology of how swiftly events are moving in the science of cloning:

• In February of 1997, researchers in Scotland announced the successful closing of the now-famous sheep, Dolly.

• Only a few months later, a national ethics commission recommended to President Clinton a three- to five-year moratorium on human cloning research, arguing that nothing would be lost by such a ban, since it would most likely take at least that long to know whether cloning could succeed -- a prediction that seems to have been proved wrong.

• The ban was not approved, and in July 1998 a University of Hawaii team produced 22 mice -- seven of which were clones of clones from the cells of a single mouse.

• Only eight days ago, a Japanese team cloned eight calves -- four of which died at birth -- from a single cow.

Until Dolly the lamb was born, it was a scientific truism that the cloning of adults was a biological impossibility. No longer.

The South Korean experiment was halted due to fear of ethical repercussions -- not because the researchers lacked the technology.

Sources: Sheryl WuDunn, "South Korean Scientists Say They Cloned a Human Cell," and Gina Kolata, "Speed of Cloning Advances Surprises U.S. Ethics Panel," both in the New York Times, December 17, 1998.