Just when zoo officials and panda fans had about given up, Ling-Ling and Hsing-Hsing have renewed their soap opera love life and are making the most of a panda passion that could result in a cub by October.

The National Zoo's celebrated giant panda couple, more accustomed to spring flings than summer romances, mated once Sunday morning and twice yesterday. After the pandas' 13-year relationship, dozens of inept attempts at coupling and two ill-fated cub births, zoo officials remain optimistic.

"Everybody is very glad to have a successful mating -- last week was very frustrating," said Elizabeth Frank, who, as the zoo's collections manager, has gotten rather caught up in the sex life of her star residents.

Ling-Ling, the female panda, and Hsing-Hsing, her at-times-awkward suitor, were a gift to the United States from China in 1972. But pandas rarely give birth in captivity, and a successful panda birth here would be the first of its kind in the United States.

The latest panda coupling is the apparent result of a series of "follicle-stimulating" hormone injections zoo officials began giving Ling-Ling two weeks ago after she failed to start her mating cycle, which for the last three years has occurred in mid March.

"The shots certainly appear to have worked," said Frank.

The pandas began flirting and exhibiting courting behavior last Monday, and by Friday, according to Frank, the premating activity was "very intense."

The pandas mated at 5:45 a.m. Sunday, and again -- and again -- yesterday, at 7 a.m. and 8:35 a.m., respectively, a mating record for them. The pair met again yesterday for a late afternoon rendezvous but without similar mating success, the zoo reported.

How long they'll be carrying on like this is anybody's guess. A normal mating cycle, Frank said, is "five to seven days, and today is day nine."

Ling-Ling, who suffered a near-fatal kidney infection in late 1983, was given a thorough physical June 12 and found to be in "excellent condition," according to a zoo spokeswoman. But veterinarians, after examining the results of a laparascopy, or scan of her reproductive track, discovered undeveloped follicles and decided to try hormone injections.

Ling-Ling is 16 and subject to the biological clock like all females, but zoo officials say pandas in China have bred into their twenties.

It's too soon to tell whether these latest mating efforts have been successful, officials say. Pandas, they report, have "delayed implantation," which means it can take 97 to 167 days before their cubs are born. The earliest that panda watchers can expect a cub, assuming one has been conceived, would be the first week in October.

The pandas first mated successfully in 1983. Ling-Ling has given birth twice. One cub died of respiratory failure shortly after its birth, and a second was stillborn last year.

Whatever the outcome, zoo officials are encouraged by the frequency of couplings this mating season. Ling-Ling is showing more interest in her partner, and Hsing-Hsing is showing more ability, particularly for a panda who spent nine years trying to establish what the zoo calls "an effective posture."