Congress is lumbering in its usual slow way through the controversial reauthorization of the Endangered Species Act. The effort should have been given some impetus last week, when a small band of bird lovers in Baraboo, Wis., showed what immense effort it takes to try to rescue a single species that has been brought to the brink of extinction.

After six years of trying, this group finally succeeded in increasing by one the world's known whooping crane population of about 100 birds. The new crane's mother, Tex (birds' sex is not evident at birth when humans tend to name them), was stimulated to ovulate through six weeks of arduous courtship dancing. Dr. George Archibald was in constant attendance at this rite.

Several times, Tex laid an egg but it proved infertile. One year, she produced a fertile egg, but the shell was too thin, and the chick didn't hatch. This year, Dr. Archibald decided to make one last, all-out effort. He camped out with Tex, walking with her, helping her build a nest and regularly performing the long--and for a human, tiring--courtship dance, complete with whoops. With the help of sperm flown in regularly from the Patuxent Wildlife Center in Maryland, it worked. But again the egg was too thin-shelled. Desperate measures to save it --including immersion in a tank of water--succeeded. They named the chick Gee Whiz.

Tex's parents are both dead, so she is the last repository of her particular genes, and in such a tiny population as the whooping cranes now are, the preservation of those genes in Gee Whiz adds substantially to the genetic diversity needed to keep a species healthy. This success, and years more of similar heroic efforts may yet save the whooping cranes.

Other species have not been so lucky. Extinctions are occurring at the rate of one species every day. By the year 2000, scientists fear that as many as 20 percent--1 to 2 million species--of the plant, animal and microbial species now on earth will have diappeared. Species have become extinct ever since life appeared on this planet, but never at rate remotely approaching this one. Gee Whiz's birth is one tiny step in the other direction. Prompt passage of the Endangered Species Act would be a bigger one.