National zoo officials yesterday officially announced an end to their exhaustive 'round-the-clock panda watch, saying that a false pregnancy had prompted Ling-Ling, the zoo's female giant panda, to behave as if she were expecting.

Early next month, Ling-Ling will be returned to her routine at the panda house, after holding zoo officials and much of Washington in suspense since late March.

"To say we are bitterly disappointed is an understatement," said zoo director Theodore Reed.

The longest known gestation period for a giant panda is 163 days. Counting back from March 21, the last of three days Ling-Ling was artificially inseminated, time runs out on Monday, when the cameras will be turned off and the watch officially ended.

Since mid-July, zoo staff and volunteers have logged 10,084 hours of watching Ling-Ling on closed-circuit television to gather evidence of behavior that would indicate if she were pregnant and hopefully to get a rare opportunity to see a panda birth.

Hopes heightened early this month when Ling-Ling showed classic signs of pregnancy--nest building, genital licking and loss of appetite--all preceded by changes in her hormone levels.

But her body did not begin to change in ways that would indicate she was preparing for motherhood. "I think we are probably dealing with a false pregnancy," a phenomenon common to other mammals, said Devra Kleiman, the zoo's chief of zoological research, adding that there are no indications of a miscarriage.

Director Reed said the zoo's male giant panda, Hsing-Hsing, will be urged again next spring to mate with Ling-Ling--backed up by more artificial insemination.

"Failure begets failure," Reed said of Hsing-Hsing, "and in six years he still hasn't learned how to do it."

Experts say Ling-Ling, 13, still has about six to eight cub-bearing years. "We will continue to try," Reed said. "We'll never quit trying."