When Bill Xanten started his long association with the National Zoo in 1956, the collection was huge -- but most of the animals lived in small yards and tiny, spartan cages, some dating to the late 1890s. There were no education programs, no scientists, no curators.

"The zoo was a mess," said Xanten, a former zookeeper who is now general curator for animal programs.

In 1958, after the fatal mauling of a toddler by a lion, Congress came to the financial rescue. Funding responsibility shifted from the District to the Smithsonian Institution, and a long-term plan to remake the zoo was set in motion.

In many ways, Xanten said in a recent interview, the National Zoo is at a similar crossroads today, and in need of a similar infusion of money.

The zoo, he said, "got crucified" last year with accounts of questionable animal deaths. But those deaths also put the spotlight on serious problems. The zoo had become "a stepchild of the Smithsonian" and "was falling apart," Xanten said, attributing deteriorating facilities and a stagnant collection to benign neglect.

The zoo's operating budget, which had been relatively flat in recent years, was $19.1 million in fiscal 2004, with the Smithsonian picking up expenses for additional facilities and maintenance staff. The capital budget was $28.2 million. In fiscal 2005, the zoo has requested $17.8 million for operating expenses and $21.5 million for capital improvements.

Xanten, 66, who grew up in Northwest Washington and now lives in Potomac, always wanted to be a zookeeper. After high school, while attending college at night, he took a job as a zoo gardener just to get his foot in the door. His forte was reptiles, but he had keeper assignments with birds and mammals as well.

In 1967, he turned down the job of head keeper so he could move into administrative and curatorial work.

Xanten arrived on the cusp of a sea change for the National Zoo and other U.S. animal parks. Beginning in the 1960s, exhibits slowly were transformed from barred, forbidding facilities into more open showcases, where the animals were contained by noise-reducing glass or by wet or dry moats. The introduction of the dart gun made it possible to administer anesthesia and antibiotics with less trauma to the animals than when they had to be physically restrained.

The zoo's mission also expanded to include conservation and science, with an emphasis on breeding and studying the animals, especially endangered species, not just displaying them.

To Xanten, it was a golden era. Theodore Reed was zoo director and S. Dillon Ripley, an ornithologist, headed the Smithsonian. The two got the funds to remodel existing exhibits and build new ones, upgrade the zoo staff and open the Conservation and Research Center in Front Royal, Va.

"The zoo went from a failed facility to a world-class structure," he said. "It was an exciting time."

But in 1996, amid budget cuts, Xanten and others took a Smithsonian buyout. The zoo, he said sadly, lost a curatorial staff with nearly 220 years of combined experience. He busied himself with consulting work and a hardware store job until last year, when Director Lucy H. Spelman asked him to return to help the zoo with its latest crisis.

Since then, he has worked to rebuild the collection. He likes small mammals, especially fennec foxes, a North African species with huge ears. But his favorite animal, the Indian rhinoceros, is no longer exhibited at the zoo, and he would like to bring it back.

Xanten said he worries that the "slow erosion" of science and budget cuts is hurting research programs and could imperil the "incredibly valuable" conservation center in Virginia.

"The zoo is going to survive," he said. "The biggest concern is how Congress will look upon us over the next few years. . . . I hope the eyes are now open and stay open."