Ling-Ling, the National Zoo's female giant panda, gave birth early yesterday to a 4-ounce cub, whose lusty squeals signaled its apparent good health and whose continued survival would reward zoo keepers with the first successfully bred giant panda in the United States.

The cub's aging mother immediately cradled and licked the new arrival, exhibiting what zoo officials called "normal maternal attentiveness" toward the 5-inch-long infant.

"She's doing everything right," said one keeper.

The birth, at 3:33 a.m. in the zoo's popular Panda House, elated zoo officials, some of whom were beginning to wonder if Ling-Ling, 18, and her mate, Hsing-Hsing, 17, would ever again become parents. The celebrated panda couple produced one cub in 1983 that died three hours later of pneumonia contracted before birth, and another cub in 1984 that was stillborn.

"We just have to take it day by day," said Lisa Stevens, the zoo's collection manager. "The baby appears to be healthy -- it certainly has a healthy pair of lungs."

Stevens watched the birth on a closed-circuit television monitor and later, at a news conference, narrated a videotape replay of the cub's arrival. She said Ling-Ling had been exhibiting all the signs of impending motherhood for days -- nest building, loss of appetite, hormonal changes in her urine -- but that the zoo's panda watchers weren't really sure she was pregnant until she went into labor shortly before 1 a.m.

"We hoped she was pregnant, we suspected she was pregnant, but we didn't know until the actual birth," Stevens said.

After its birth, the tiny cub was all but lost in its mother's protective embrace. For the briefest moment, however, a little white foot was glimpsed sticking out beneath Ling-Ling's chin.

"It looks very much like a rat," said Stevens. "It's white and very, very small."

Ling-Ling and Hsing-Hsing were gifts to the United States from the Chinese government in 1972, after President Nixon's historic visit to Peking. And it is the Chinese Embassy here that will have the honor of naming the new cub -- as soon as its sex can be determined.

The embassy offered a couple of names a few years ago, in anticipation of the first panda birth, but zoo authorities weren't about to disclose them yesterday. It will take several weeks before the cub's sex is known, they said, and there is a possibility that embassy officials may want to change their mind and come up with another name.

The Panda House was closed yesterday, and zoo spokesman Robert Hoage said the new cub will not be seen in public for at least four months. In the meantime, panda lovers can view mother and baby on a special television monitor in the lobby of the zoo's education building.

Hsing-Hsing, described yesterday as a "pretty oblivious father," has a separate enclosure from his mate and can be seen when he comes out to play in the panda yard.

The giant pandas, who failed to mate at all last year, mated a record seven times in early March, and zoo officials had said then that a cub might be born anytime between July and September. In pandas, the recorded time between fertilization and birth has varied from 97 days to as long as 168 days.

In contrast to previous news about the pandas, yesterday's birth caught the city by surprise. After years of chronicling every mating success and failure, every real or suspected pregnancy, zoo officials say they deliberately decided to "low-key" it.

"We kept Ling-Ling in her normal routine, with as little disruption as possible," said Hoage. The usual "Panda Watch" by zoo volunteers was started about a week ago, but this time the media weren't notified.

The heartbreak of the two unsuccessful births, and embarrassment two years ago when a much-touted pregnancy turned out to be a false alarm, also may have influenced the decision to keep a low profile this time.

The population of wild pandas is endangered and continues to decline, according to the World Wildlife Fund, which puts the number at between 800 and 1,000. About 50 giant pandas are in captivity in China and another 17 in zoos outside of China.

Yet the pandas are extremely difficult to breed in captivity. Yesterday's birth increased the number of pandas successfully bred in captivity to six; the others were one in Madrid, one in Tokyo and three in Mexico City.

Since receiving the panda pair 15 years ago, the National Zoo had gone to just about any lengths to help them produce a cub.

But the couple wasn't exactly a match made in heaven, especially at first. During early mating attempts, Hsing-Hsing, truth be told, was an inept lover, and Ling-Ling wasn't particularly interested. Their fruitless efforts became an annual rite of spring -- and an annual occasion for jokes about the perils of panda passion.

Along the way, zoo officials tried playing Cupid. They experimented with artificial insemination, left them alone together for longer periods, installed an exercise course in their yard and prodded Ling-Ling with hormones. They even imported a male panda from London, but Ling-Ling didn't like him any better.

When Ling-Ling and Hsing-Hsing finally consummated their relationship, the resulting ill-fated panda births only added to the discouragement. Also, in December 1983, Ling-Ling nearly died from a kidney infection, and veterinarians resorted to blood transfusions and massive doses of antibiotics to save her.

Some animal lovers suggested that Ling-Ling was getting too old to be a mother and ought to be left alone. But the zoo, officials said yesterday, never lost hope.

"I was just thrilled," said Stevens, describing her thoughts as she watched the birth. "I wanted to jump up and down and call everyone. I couldn't keep my eyes off the monitor."