The lovers met in passion beneath the willow trees in the soft gray dawn.

He bit her ear.

She slugged him, then shoved him down a hill.

Then they joined--almost--in a ferocious 535-pound embrace. Of panda love.

Hsing-Hsing and Ling-Ling, America's two giant pandas whose fruitless mating attempts have become an annual rite, went at it again yesterday for their sixth consecutive season at the National Zoo.

But once again, despite a new strategy by the zoological matchmakers, the attempted liaison was a washout. The action was fast and furious, but the outcome for one of Washington's most popular romantic couples was again disappointing.

The official verdict: "ineffective breeding posture;" with Hsing-Hsing, the 285-pound, 11-year-old male, again bearing the sting of being labeled an "inept" lover, and Ling-Ling, the 250-pound older woman of 12, also being criticized for roughing up her mate and puzzling him with unusual tactics like standing on her head.

"It's getting as frustrating for us as it is for them--I think," said a downcast zoo director Theodore H. Reed, who was among a throng of about 40 zoologists, photographers, reporters and passers-by who gathered at 7 a.m. to await the annual panda tryst. Mating is possible only once a year, during a three-to-five-day period when Ling-Ling is in heat.

Later yesterday, after a lunch of 30 to 40 pounds of bamboo, plus honey, apples, carrots, sweet potatoes and powdered cottage cheese, the lovers tried again--and again failed, with the female seeming, if anything, more truculent.

Zoo officials said late yesterday they would try artificial insemination, and readied a team of 12 veterinary and medical specialists. A similar attempt in 1980 failed, but it will take months to determine whether this effort succeeds.

While there was considerable laughter and joking among the assembled voyeurs at Panda Gardens, there was serious concern among zoo officials, because the pair is no longer young and each passing year lessens the chance of a baby. Fertility begins about age 6 and is estimated to end in the low teens. Last year, a male panda from the London Zoo, Chia-Chia, was brought in to mate with Ling-Ling or at least spur Hsing-Hsing to amorous jealousy. Again, no luck.

"This is all fun," said zoo spokesman Ilene Ackerman, "but it is also a very serious effort to preserve a beautiful and endangered species." Pandas mated successfully in Mexico City last year, one of the rare cases of birth outside their native China, Reed said.

Since October, zoo officials here had embarked on a new plan of amatory attack. The Chinese, who gave America the pandas in 1972 as a gesture of friendship marking the visit of Richard Nixon, had advised that the animals were solitary by nature and should be kept apart, except during estrus.

However, after repeated failures, zoo officials figured that if the couple got to know each other better, they'd have a better chance of adapting to each other's moods and moves, Ackerman said. Starting with once-a-week visits of four hours' duration, Hsing-Hsing and Ling-Ling gradually increased their time together to thrice-weekly visitation, according to Bess Frank, collection manager for zoo mammals.

Yesterday, it appeared to be for naught:

Frank, armed with clipboard and stopwatch, carefully recorded every 30 seconds of sparring, wrestling, scent-marking and indifference.

They paced. They pawed. They bleated--sounding remarkably like two electronic video game machines at war. Then they grappled.

They tumbled together in the grass, rolling like an enormous furry soccer ball. But with each attempt, either Hsing-Hsing lost his balance or Ling-Ling lost her temper, several times swatting him and sending him scurrying off.

"The degree of her passion has not yet reached its maximum," Reed theorized, "It's the old buildup, you know . . . I guess the scientific term is foreplay." He faulted Hsing-Hsing, "Do you realize what he is doing to the male ego?"

Frank suggested that Ling-Ling should share the blame. "After all, she isn't very nice to him," she said,"It's like anything else, though. They just have to work out their own problems."