At 10:33 a.m. yesterday, Ling-Ling, the National Zoo's most famous resident, roused herself from a deep "rest," rolled over a bit on her backside and did a few lethargic leg lifts.

At 10:49 a.m., the giant panda lumbered to her feet, turned slightly and plopped herself into a sitting position, her back against the doorway to her den.

It wasn't much but it was enough to send zoo officials and volunteer panda watchers crowding around television monitors for a closer look. The panda's moves were duly recorded on a white "Giant Panda Checksheet," where notations about "Resting and Sleeping" are the norm.

Zoo keepers are almost certain Ling-Ling is pregnant, and they've enlisted the help of 75 volunteers for round-the-clock panda watching. This is the 15-year-old Ling-Ling's third attempt at motherhood, and nobody wants to miss anything.

What does a probably pregnant panda do all day?

"Sleep, eat and pace, and she yawns a lot, too," said Norma Cummings, 68, a retired obstetrician and gynecologist from Rockville who keeps an eye on Ling-Ling during the 10 a.m. to 1 p.m. shift.

Since late October, when zoo officials closed the Panda House and set up an observation post in the panda kitchen, animal lovers from the Washington area have been filling 56 such shifts a week. They sit in a small room off the panda exhibit area, with two refrigerators, trays of carrots, television and audio recording equipment and several panda posters and cartoons.

On one counter is a box for the "Panda Pool" for delivery date predictions -- one guess per volunteer.

"Everybody comes in with the idea that, 'on my watch, something is going to happen,' " said Nell Ball, 53, a volunteer from Vienna who keeps the official panda records and coordinates all the panda watch data.

Ling-Ling's first cub was born in July 1983, but died a few hours later from a respiratory ailment. Ball was on duty in August 1984, when a second cub was stillborn.

"You get all hyped up and then drop back down to zero," she said yesterday, recalling the sadness and disappointment. Zoo officials and other panda lovers are hoping for better results this time.

The recorded gestation period for a panda has varied from 97 days to as long as 168 days, and zookeepers think Ling-Ling is roughly 142 days into her gestation. Her first cub was born in 125 days, and the second arrived in 139.

But you can't draw conclusions or form timetables from earlier patterns, warned JoAnne Grumm, a program assistant at the zoo who is in charge of the panda watchers.

The volunteers, chosen from the Friends of the National Zoo's behavioral watch trainees, come from all walks of life, according to Grumm, but have at least one thing in common: they love animals. "We have students, a few housewives, people who work on the Hill, people who work for airlines."

Cummings relieved Clark Miller, a computer expert from Arlington. One couple lives near Baltimore. A woman who lives near Front Royal, Va., takes the 1 a.m. to 4 a.m. shift so she can drive to the zoo without getting stuck in traffic.

Ling-Ling, the oldest female panda living in the Western Hemisphere, spends most of her time sleeping or resting. Zoo watchers make a distinction because they have discovered -- using a zoom camera lens -- that the panda often has her eyes open while reclining.

But the volunteers don't dare let their attention wander. This is no place for a book, they say.

"She's quick," said Cummings.

As if to prove the point, Ling-Ling abruptly got up at one point and moved into her den, temporarily out of camera range. The four cameras were adjusted to catch her as she scratched, licked her toes, rubbed her ears and generally fidgeted before resuming her panda slump.

Cummings hurriedly scribbled. She wrote "scratch" and "rubbing her head and ears" in the grooming column.

When the panda starts building a nest, zoo officials said, it will be time to watch for another cub birth.