There's a new, unadorned look at the Panda House.

The National Zoo and animal lovers were bitterly disappointed in June when Ling-Ling, the female giant panda, lost yet another cub just as zoo officials were congratulating themselves on what looked like the first successfully bred giant panda in the United States.

The zoo has determined that the cub was healthy at birth but became infected by a common environmental bacteria. So, with the spring mating season approaching, keepers have revamped Ling-Ling's cage, clearing out the rocks and wooden structures that may have been hiding places for the organism that killed her cub.

"Her cage is practically bare now," said Lisa Stevens, the zoo's collection manager. "The idea is to improve drainage in the cage and to make it cleaner."

Ling-Ling and her mate Hsing-Hsing, who normally are kept apart, have been put together every morning since Feb. 1 to encourage their mating efforts should the female panda go into heat. Mating season is between March and June.

Pandas are an endangered species, and breeding the panda pair has been the zoo's anxious goal since Ling-Ling and Hsing-Hsing arrived in Washington in 1972, a gift from the Chinese government. After a rocky courtship -- he was clumsy, she was indifferent -- Ling-Ling has given birth three times.

The first cub died of pneumonia in 1983 after living only three hours. A second cub was stillborn in 1984. The third cub, born June 23, lived nearly four days before dying from the bacterial infection.

Ling-Ling, nearly 19, is the oldest giant panda in captivity outside of China, and the zoo is uncertain how long her cub-bearing years will last. "She is healthy and everything looks normal," Stevens said. "But she has done something different every year, and we can't really predict when she'll go into heat or what she'll do."

There is other zoo news that is less speculative than panda procreation.

In May, the zoo will open two new exhibits, one for its gibbons and another for waterfowl. The gibbons, the most acrobatic of the primates, will be getting a large mesh enclosure near the Bird House that will give them plenty of room to climb and swing, according to Mike Morgan, a spokesman for the zoo.

And the zoo, which has expansion dreams bigger than its federally provided budget, is about to launch a private fund-raising campaign for other pet projects.

First on the list, according to Elsa Yablonski, director of development, is a $2 million Australian Pavilion, with animals native to that continent. Qantas Airlines has already signed on as a patron, and some zoo officials leave this week for Australia to begin preparing for the exhibit, which the zoo hopes to open at the end of 1989.

Fund raising is also under way for half of the $12 million the zoo needs for its planned Amazonia rain forest, an exhibit scheduled to open in 1990. A children's zoo is also on the wish list, though no date or price tag has been set.