After weeks as the subject of intense observation and solictious speculation, Ling-Ling, the National Zoo's cuddly female panda, made her fall public debut yesterday, still the liberated woman and quite childless.

Zoo officials called off their 24-hour closed-circuit television watch of Ling-Ling, ending another chapter in the sad sexual history of Hsing-Hsing the park's would-be papa bear.

Folliwing her artificial insemination last May, Ling-Ling should have shown some results of pregnancy by now, a zoo spokesman said, So yesterday she was permitted out of her matermity suite while authorities ponder ways to end once and for all her days of fruitless love.

"The building is going to remain closed," said mammologist William Xanter, acknowledging a slight chance Ling-Ling may yet surprise her keepers. "they will put her in in the evenings, just as a percautionary measure."

As a result of the latest failed attempt, Hsing-Hsing may have to yield to his sorry track record in the affair and settle for "just friends." The question of Ling-Ling's childbearing may be up to a more prodigious--and possibly imported -- mate.

Female pandas are believed to go into heat but once a year. After previous attempts at mating Hsing-Hsing and Ling-Ling failed to bear offspring, zoo officials inseminated her artificially May 17 and 18 with Hsing-Hsing's sperm.

Normally the panda gestation period lasts 118 to 168 days, with most observed births around 135 days.

As that day -- Sept. 26 -- drew closer, six dozen volunteers from FONZ (Friends of the National Zoo) began a 24-hour vigil in three-hour shifts. Expectant pandas show few physical signs of pregnancy, so when Ling-Ling began to pace and fidget in her nest, observers fell into a state of nervous anticipation.

Lately, however, hopes dimmed with each passing day. Scientists still aren't sure what Ling-Ling's behavior might have meant.

"the signs of pregnancy are very similar to the physical signs of estrus," Xanter said. "we went through the same thing two years ago, when she started to act a little funny and was seen to make a nest."

Because Western scientists have relatively little experiences with the Chinese imports, they remain baffled by some forms of behavior, Xanter said. Zoo officials are still wondering why Hsing-Hsing's sperm count was lower this year than last, though the trend is believed to be widespread among his human counterparts.

Even before this year's attempt at impregnating Ling-Ling artificially -- which included mixing this year's semen with samples frozen last year -- officials considered trying with another beast, Xanter said. Hsing-Hsing may find himself on involuntary leave next spring if authorities decide to exchange him with a more promising brute, possibly from Mexico or London.

"you have one shot at it. You miss it, and that's it. And that's what we've been faced with for the last six year," Xanter said. "we're just going to hold tight and make plans for next year."