Thousands of giant-panda lovers got coveted tickets yesterday to see the National Zoo's new cub next month -- and thousands more did not, much to their distress.

More than 13,000 free, timed-entry passes to see the cub between Dec. 8 and Jan. 2 were snapped up by about 11 a.m., two hours after the zoo began making them available through its Web site. But many people could not access the page to make a reservation to visit the Panda House, despite their most determined efforts.

"I stayed on my computer -- like a fool -- from 9 a.m. until a little after 12 p.m.," said a disappointed Brenda Sippel, a self-employed artist who lives in Potomac. "I really wanted them for my grandchildren."

The zoo said it was sorry for any problems on its Web site, which became overwhelmed with people eager to see the black-and-white bear, Tai Shan, when he finally makes his public debut. Tai Shan is the first surviving giant-panda cub born at the animal park.

"We apologize for the inconvenience folks had trying to get passes," said Matt Olear, a spokesman for Friends of the National Zoo, the zoo's support organization, which handled ticket distribution. "But we want people to know that this is not the end. There will be plenty of opportunities later to see him."

Not everyone was grabbing the tickets for themselves. Hours after the zoo announced that no more were left, some of the free tickets turned up on eBay, going for $75 and up.

"These were incredibly difficult to get and this will be such a wonderful opportunity to see this little baby!" said one listing, which added that a portion of the proceeds would go to a nonprofit group.

"It's going to happen," Olear said, expressing disappointment with the profiteering. He cautioned that the zoo will be checking identities of Panda House visitors to make sure that their names match those on the reservations.

The zoo's Web site was so deluged yesterday that, for a time, both its regular Web site and that of the Smithsonian Institution, its parent organization, could not be accessed.

"There was so much strain on the system that people were having a hard time having the [ticket] page come up," Olear said.

Initially, visitors to the Panda House, about 50 at a time, will be admitted for 10-minute intervals between 11 a.m. and 1 p.m. daily. The hours are expected to be extended early next year as Tai Shan and his mother, Mei Xiang, become more comfortable with crowds near them.

The zoo plans to make about 60 tickets available daily for same-day visits. But Olear said these will best serve out-of-town visitors who may not have heard about the ticketing system. Same-day tickets, he stressed, should not be seen as "a viable alternative" to having timed-entry passes.

The focus of all this fuss got his 12th veterinary exam yesterday. The cub, now more than 4 months old, weighed 19.2 pounds and measured more than 31 inches. He received a rabies vaccination and spent a good portion of the day in the public exhibit area, climbing over the rock work or trying to nap on it.

"He's a climbing fiend," assistant curator Lisa Stevens said. "He's climbing all over the rocks, or he's climbing on his mother. And when he's not climbing on her, he's chewing on her. . . . She lets him treat her like a giant chew toy."

The chances to see Tai Shan will be better next year as the cub gets older and more independent. But Stevens warned that once the cub starts to go outside, he could choose to hide under a bush or climb a tree, making him harder to spot in the yard.

"He's a little panda that has to be free to grow up," she said. "Everyone is going to have to understand and accept whatever viewing opportunities occur."

For links to webcams of the panda and more information, go to www.washingtonpost.com/metro.

Zoo veterinarian Ellen Bronson checks 4-month-old Tai Shan's teeth. Yesterday's exam also included a rabies vaccination. Tai Shan is the first surviving giant-panda cub born at the animal park.