Three days after it was born, the National Zoo's giant panda cub continued to assert itself with loud squawks and yips, but the chief veterinarian at the animal park said yesterday that it could be months before the tiny, fragile newborn is out of danger.

The mother panda, Mei Xiang, spent much of the day yesterday trying to doze, lying on her side or her back or sitting up with her head slumped over her chest. When her infant squealed, though, she quickly jerked herself awake and changed position until the cub quieted. It could be weeks before Mei Xiang emerges from the back den of the Panda House where she gave birth early Saturday.

Panda cubs, born after a three-month gestation period, are blind at birth and much less developed than human newborns. Panda newborns have no fur, are vulnerable to infection and are entirely dependent on their mothers' care for several months. The Panda House will be closed to the public for at least three months so mother and infant can bond, but the outdoor yard will be open, and the male panda, Tian Tian, is sometimes there.

Mei Xiang, a first-time mother, seems to be attending to her infant's every need, zoo officials said, but they emphasize that the cub is still at risk.

"We will not [know] that the cub is out of danger for several weeks to months," Suzan Murray, the zoo's chief veterinarian, said during an online chat yesterday on The Washington Post's Web site. "This will be determined by the cub's growth, activity, and age."

In an appearance on ABC-TV's "Good Morning America," Murray declared: "We passed a couple of important hurdles. We won't be exhaling for a while."

Carmi Penney, curator of mammals at the San Diego Zoo, which has had two successful panda births, said yesterday that National Zoo keepers are right to be cautious. He pointed out that the Chinese have a tradition of not naming panda cubs until they are 100 days old, which is "the critical period before guaranteed survival."

"That's about three months," he said. "I think it's a safe figure. Three months, when you look at carnivores, is when they get past the infantile susceptibility to a number of diseases."

In San Diego, keepers looked for strong cries from cubs as signs of vigor, Penney said. They also monitored closely the amount of attention the mothers were giving because so much was dependent upon their care. National Zoo keepers have said they are taking the same approach. Especially with the first cub, Penney said, San Diego's keepers were anxious anytime they heard or saw new behavior.

"We were probably alarmed at everything the first time around," he said. "None of us had the intimate experience with this. We were cautious to an extreme, just like I think the folks at National are."

During its first panda birth, San Diego did have expert assistance from a Chinese panda keeper, who had come from the Wolong reserve "to give us guidance in what we are looking at." San Diego, in turn, sent one of its panda-nursery specialists to the National Zoo on Sunday to help out for a while.

"It didn't keep us from worrying," Penney said of the advice from the Chinese keeper, "but it was helpful in establishing some baselines."