The folks at the National Zoo know all about giant pandas. They know why we like them (big eyes and high-domed foreheads like those of human children), when they become sexually active (between the ages of 4 and 6), even their favorite muffin.

"Hsing-Hsing really likes the blueberry muffins from Starbucks," Lisa Stevens, associate curator, said yesterday, describing the snack preferences of Hsing-Hsing, the zoo's aging giant panda.

But one thing the zoo doesn't know is whether China will take it up on its recent offer: $2.5 million for panda research and conservation programs in exchange for a 10-year loan of two young, captive-born pandas.

"We are very optimistic," said Benjamin B. Beck, associate director and a member of the zoo delegation that returned from China last week after negotiating with government officials there about getting new pandas.

The zoo's money offer is much less than those of other zoos, and some have speculated that its prospects are dim. Zoo Atlanta, for instance, has agreed to pay China $1 million a year in exchange for the loan of two pandas for 10 years. San Diego pays $1.2 million a year on a 12-year contract that started in 1996.

"I'm told we were well received," said Robert J. Hoage, chief of public affairs at the zoo, which charges no admission. He argued that the zoo's $250,000-a-year offer factors in other benefits to China. "We believe there is a lot of value added here," he said. "We are offering years of expertise in caring for pandas and some technical assistance they would be hard-pressed to find elsewhere."

Zoo officials said they also hope the Chinese agree that there is special nation-to-nation significance in making sure the famed, endangered giant panda is represented in the U.S. capital.

"The pandas would be great ambassadors . . . symbols of the friendship between our two peoples," Beck said.

The collaborative educational and research projects outlined during the delegation's eight-day trip to China included behavioral, endocrine, genetic and population studies; computer modeling; satellite monitoring; and extensive conservation training and assistance.

Friends of the National Zoo, the zoo's fund-raising auxiliary, has pledged to raise the $2.5 million.

The zoo's search for new pandas is deemed particularly urgent because Hsing-Hsing, its sole surviving panda from the pair given to the zoo in 1972, is now 28 and suffering from arthritis, anemia and kidney failure. His mate, Ling-Ling, gave birth to five cubs, none of which survived.

China no longer gives away pandas, and loans of pandas are now carefully controlled by the Giant Panda Plan, which is supervised by the American Zoo and Aquarium Association. Driving this restraint is the growing concern about the survival of the species. Habitat loss and breeding problems have reduced the number of pandas in the wild to about 1,000 scattered across mountainous south-central China.

Hoage said the zoo expects a response from the Chinese next month.

A Chinese Embassy spokesman said yesterday that reaching a panda agreement with Washington would be helpful, given the strained relations between the two countries since NATO's bombing of the Chinese Embassy in Belgrade and allegations that China stole U.S. nuclear secrets.

Yu Shuning told the Associated Press he could not speculate on whether officials in China will agree to lease the pandas. But he wished the zoo success.

"We think the panda is not only a national treasure of China but also of the whole world," he said.

CAPTION: Girls stretch over a fence to try to glimpse a sleeping Hsing-Hsing at the National Zoo. Later, Hsing-Hsing emerged from his sleeping area to eat for the crowd. The zoo is hoping China will agree to lend it two more giant pandas.

CAPTION: Hsing-Hsing at the National Zoo, which reported on efforts to get two more giant pandas.