After six unsuccessful mating seasons with her live-in lover, a fling with a visitor from London, and two desperate years of artifical insemination, Ling-Ling is pregnant.

Maybe.

No one will know for certain whether the National Zoo's 250-pound female giant panda is actually expecting until the cub, if there is one, arrives, zoo officials said yesterday. With pandas, it's hard to tell.

But just in case the stork is on the way, zoo officials announced that they will close the Panda House Tuesday for at least a month to give the might-be mother some peace and quiet. Visitors will have to be content with peeking at one of the zoo's most popular attractions by way of closed-circuit television.

"We have high hopes, but we won't know anything for at least three or four weeks," he said. Zoo spokesmen say that if Ling-Ling is pregnant, she will give birth early next month.

Zoologists will be watching Ling-Ling on five cameras 24 hours a day, looking for indications of pregnancy--a change in eating habits, a reluctance to climb up on the rocks in her den, a swelling of her nipples.

"At the present moment, we are taking precautions in case she is pregnant and does have a baby," said zoo director Theodore Reed. "Since we have no way of telling whether or not she is pregnant, this is our insurance policy."

Yesterday Ling-Ling was keeping the news to herself as she lounged in her air-conditioned quarters munching on stalks of green bamboo as throngs of people looked on.

Hsing-Hsing, as is customary when it isn't mating season, is separated from her and will remain alone during the panda watch. Visitors can see him when he goes outside in the early morning.

Pandas rarely give birth in captivity, experts say. If Ling-Ling does, she'll be the first giant panda in the United States to accomplish that.

Zoo officials are especially optimistic this time, said Dr. Robert J. Hoage, Reed's special assistant, because a new technique was used to determine whether the panda's eggs were in position to be fertilized before she was artifically inseminated when she went into heat this spring.

For the last six years, Ling-Ling's road to motherhood has been an uphill struggle marked with disappointments and U-turns.

Her roommate and unwieldy lover, a 285-pound male giant panda named Hsing-Hsing, has been less than inspiring in the hay. Following each unsuccessful mating season, zoo officials hoped he would eventually become more adept at the mating game. But no.

Year after year, he repeatedly frustrated Ling-Ling's annual reproductive urges with clumsy advances that concluded in his failure to "align himself with Ling-Ling in an effective breeding posture," Hoage said. "He has not performed adequately."

So in 1980, Ling-Ling was artifically inseminated. Nothing happened. Last year, Chia-Chia, another male giant panda, was flown in from the London Zoo to take Hsing-Hsing's place in the annual ritual. Once again, nothing. They found themselves incompatible, Hoage said.

In March, zoo officials decided to use artifical insemination again after the panda couple failed once more to mate. Hoage said a zoo medical team used an optical probe called a laparoscope to look directly at Ling-Ling's ovaries, to determine the exact time that fertilization would be likely to occur. It was the first time such a procedure has been performed on a panda in heat.

For three days, Ling-Ling received frozen sperm from London Zoo's Chia-Chia and fresh samples from Hsing-Hsing.

"Right now we feel we did a terrific job this year," Hoage said. "If we don't get a pregnancy we will be disappointed. We won't be quite sure how to improve on our technique."