Two years ago the majestic, ancient bird that once roamed the skies of the continent was down to its last 20 members, a dying species destined to fade like the summer thunderstorms the Indians said carried the sound of its giant wings.

Today, the California condor has rebounded from the brink of extinction. In less than a year, a once-maligned federal-private project has increased the bird's world population by 33 percent. Seven young California condors, four the first hatched in captivity, are growing rapidly in a breeding program whose success has international zoologists celebrating.

"We're light years ahead of where we were," said Pete Bloom, one of a team of National Audubon Society scientists working with the U.S. Fish and Wildlife Service and two California zoos to save the largest land bird in North America.

In a private refuge in the hills above the Wild Animal Park, the Zoological Society of San Diego's 1,800-acre reserve at San Pasqual, zoologists recalled some anxious moments in the early lives of the four ungainly chicks named Sisquoc, Tecuya, Sespe and Almiyi.

"The first month was critical," zoologist Don Sterner said. But now they are so strong, he added, that "there is nothing that can kill them, unless someone killed them deliberately."

To remove that possibility, the condors are kept with other large vultures in a complex of screened and shaded pens behind a tall fence topped with coils of barbed wire.

Park security guards patrol regularly, tourists are kept away and special visitors may look at the condors only from the side of the complex opposite their 80-by-40-by-24-foot cages. Security for three new condors at the Los Angeles Zoo, another participant in the project, is equally tight.

If the condors ever go on display, "it would be a place where you could only see them from a distance, perhaps with binoculars," Sterner said.

Even the staff who feed them and clean their cages make only two quick visits a day. "We do not want them to get too used to people and affect their relationship with their own kind," he said.

The snatching and captive breeding of the rare birds has shaken relationships between usually friendly environmental groups.

The Sierra Club and northern California's Golden Gate chapter of the Audubon Society have vigorously opposed the condor project, particularly its request for state permission to capture three more adult condors, one more chick and perhaps six more eggs for rearing in captivity.

Mark Palmer, a zoologist who heads the Sierra Club condor task force, said the federal-Audubon Society project has not revealed when or how it will return the captured condors to the wild.

"A lot more work should be done on beefing up range protection," he said.

Palmer and other environmentalists have insisted that the project concentrate first on protecting condors in the wild from hunters, power lines, pesticides and other man-made intrusions thought to have cut so deeply into their numbers.

Scientists, who tracked two condors with transmitters on their wings for a year, say they still have no new clues to what is killing the giant birds. Bloom said the younger condors range far north into the Sierra foothills at speeds greater than anticipated. Growing knowledge about their favorite spots for finding dead calves and deer may help unlock the mystery of their brush with extinction.

The state fish and game commission has given permission for five more birds to be netted in Los Padres National Forest and fitted with tiny transmitters. A special receiver attached to an old skeet shooting tower in Bakersfield will monitor them.

At Wild Animal Park, all that an ordinary visitor may see of the condors is a videotape of Tecuya breaking out of her shell in April, followed by brief shots of her growth since.

All four condors were hatched in incubators at the San Diego Zoo's Avian Propagation Center. Nestled in portable incubators built for human babies, the chicks were taken by ambulance with nurses in attendance to the park 20 miles north of San Diego.

The birds have flourished on the diet favored by their kind since the Pleistocene Epoch. Young condors are fed "pinkies," the bodies of newborn mice served on a small platter by a puppet head that looks like an adult condor.

Older birds devour day-old farm chicks, rats and horse meat brought to the park frozen and then thawed in the sun. Young California condors also get helpings of predigested vulture regurgitant to accustom them to the bacteria that all carrion-eaters encounter.

Condors reach full growth in a year, and sexual maturity in about five years. At about 5 months, Sisquoc--the lone male condor here--weighs 21 pounds. Tecuya, a week younger, weighs 16 pounds. Sespe and Almiyi are about 3 months old and weigh 15 pounds each.

Seen on the videotape as a fuzzy white chick with a bright yellow head and neck, Tecuya now is a brown-headed, brown-feathered bird. She and Sisquoc recently took their first brief flights.

The Los Angeles Zoo has two young males captured in the wild--Paxa, age 2, and Xolxol, age 1--along with a recently captured chick, Cuyama, now 3 months, who has not had the blood test to determine gender. They are joined by Topatopa, a 17-year-old condor who has been on display at the zoo for years, but has been removed to the zoo's remote "Condorminium" to become familiar with his new companions, and hopefully find a mate.

Most of the condors in captivity may never be released to the wild, but project scientists say any young they produce eventually will go back to the California cliffside homes of their few relatives, including the only four known nesting pairs.

The zoologists who peer at their nests from hidden blinds talk like teen-agers discussing their favorite soap opera: the preoccupation with sex is intense. Bloom has noticed, with much approval, that one of the radio-tagged birds, a male known as AC-2, has been spending time with another, still sexually immature, condor.

"They feed together," Bloom said. "He may have a girlfriend in hand."