They were treated like pop idols, except they were shipped in travel crates. Adoring crowds and television viewers watched Thursday as American-born giant pandas Mei Lan and Tai Shan were loaded onto a special cargo jet for a flight to their new homes in China for breeding. Normally placid, 3-year-old Mei Lan from Zoo Atlanta whirled and paced in her crate as flashbulbs popped. Tai Shan, a 4½-year-old born in Washington, hid at first but was drawn into view as his longtime keepers at the National Zoo knelt silently at his crate to say goodbye, hand-feeding him slices of apples and pears. China lent Tai Shan’s and Mei Lan’s parents to U.S. zoos for conservation, and now their cubs will become part of a breeding program in their endangered species’ native land. About 1,600 giant pandas live in the wild, and another 290 are in captive-breeding programs worldwide, mainly in China.(19 images)