Hsing-Hsing, the surviving member of the National Zoo's celebrated giant panda couple, is seriously ill with kidney dysfunction that may not be reversible, zoo officials said yesterday.

The black-and-white male panda -- the most famous zoo animal in the world and one of fewer than 1,000 of the endangered species worldwide -- has charmed visitors since his arrival at the zoo 27 years ago. One of two pandas given to the zoo by the people of China during the Nixon administration, he is nearing the end of what has been a long life for a panda. This decade alone, he lost his mate, had cancer surgery and was put on anti-arthritis drugs.

The panda's kidney problems were discovered May 15, when veterinarians examined him under anesthesia because he seemed lethargic and had lost both weight and appetite. When healthy, Hsing-Hsing (pronounced Shing-Shing), 28, ate more than 20 pounds a day of bamboo, fruit and a specially mixed "panda gruel."

An analysis, including sonograms and a blood sample, revealed "severe kidney dysfunction" that "may not be reversible," according to zoo spokesman Robert Hoage.

The Panda House has been closed periodically since then to allow the animal to rest or receive treatment, Hoage said. Visiting times are now unpredictable, and a sign is posted near the exhibit when it is closed saying Hsing-Hsing is "not feeling very well."

Zoo officials say they are not ready to give up on their most popular attraction, whose name means "shining star" in Chinese. Hsing-Hsing, they say, has proven amazingly resilient. Yesterday, for example, he ate a small amount of bamboo -- a good sign, but he "remains in very serious condition," Hoage said.

"It's sort of a day-to-day situation," Hoage said. "He seems to revive and do reasonably well, and then there's a decline, and a revival, and so on."

Hsing-Hsing's kidney failure seems to be related to his advanced age, Hoage said. And his age is a reason that extreme measures such as dialysis treatment or a transplant cannot be tried. The animal, he said, would have to be put under anesthesia for either procedure, a huge risk for an elderly animal.

Hsing-Hsing and his mate, Ling-Ling, arrived at the National Zoo in green lacquered crates on April 16, 1972, accompanied by armed guards. The gift was a happy byproduct of Nixon's historic visit to China, and the animals were an immediate hit with the public.

Attention turned quickly to the possibility of a baby panda, but it was not to be. The pair began trying to mate in the mid-1970s, but did not successfully do so until 1983. They had several cubs, but none survived more than a few days.

After the birth of her first cub in 1983, Ling-Ling developed a serious kidney infection, surviving only because of antibiotics and a blood transfusion from her mate. Dialysis was considered -- Ling-Ling was a youngish 12 at the time -- but it was not needed.

Ling-Ling died in 1992, of age-related heart failure. After she died, the zoo took down a fence that often kept the animals apart.

Hsing-Hsing increasingly began to show his age after that. Two years ago, he was diagnosed with testicular cancer and arthritis. Veterinarians removed a testicle, and the cancer has not recurred, Hoage said. Anti-inflammatory medication helped with the arthritis; Hsing-Hsing perked up noticeably after he began taking it, until lethargy returned last month.

Pandas, which are members of the bear family, are native to the high-altitude damp forests of China. Their numbers are dwindling because the bamboo forests are being chopped down, poachers kill them for their pelts and they have low reproductive capacity.

In the wild, they live about 15 years, but in captivity, they survive on average about 10 years longer. Hsing-Hsing is believed to be one of the longest-lived giant pandas in the world.

CAPTION: Hsing-Hsing nibbled bamboo after cancer surgery in 1997. He now faces a new illness.