"El Macho," his friends call him. More formally, he is known as Pe-Pe, one of the few pandas in captivity outside of China and the only one in the Western world who seems likely to be a father anytime soon, especially since the British panda called in by the Washington National Zoo turned out to be such a boorish, brutish failure.

Officials here at the Chapultepec Zoo aren't saying that Pe-Pe's consort, Ying-Ying, is pregnant again. But they say it is very likely. Her prime time for lovemaking came last month and she and Pe-Pe, according to those who know, did a lot of it.

The zoo administrator, Gabino Vazquez Ramirez, said no one is going to know for sure if Ying-Ying is in the family way until she delivers -- or doesn't. But the prospective date of July 22 is already marked on Vazquez's calendar, and this week he was clearly excited about the chances. By some estimates there may be only 300 giant pandas left in the world, and Mexico's are the only ones in captivity that seem inclined to do anything about their breed's population problems.

Unlike Washington's pandas, who are more or less officially estranged, Pe-Pe and Ying-Ying live comfortably together in the same quarters. during their six years here (virtually their entire lives) they have established quite a rapport.

Last August Ying-Ying gave birth to the first panda ever born outside of China. Pandakeepers elsewhere noted the event with awe -- and perhaps a twinge of jealousy.

"Mexico has lucked out completely," one official at the Washington National Zoo reportedly commented at the time. "Their pandas are young and just barely sexually mature."

But baby Xinli was killed only eight days after birth, before it weighed even a pound, before it even looked like a panda.

The zoo administrator's face darkens as he recalls the event. "People who don't know pandas criticized us," he said. They claimed the baby should have been taken away from Ying-Ying for its own protection. Nonsense. No mother ever loved a daughter more. "In the first four days," said Vazquez, "she didn't put down the baby for a moment. Not even to eat."

But Ying-Ying, perhaps upset by all the attention and the visitors (her friends tend to be particularly harsh when they talk about the politicians who flocked around to bask in her maternal glow) finally snuggled the naked little panda to death.

This time around, Vazquez says, there will be no visitors. Even Pe-Pe is going to be moved to separate quarters three days before the appointed date. He gets depressed when he's alone, but that's just the way it will have to be. Meanwhile, mother and child will be watched over closed circuit television. Press and dignitries can see them that way if they want.

But the question remains: How come these pandas do what those in other zoos don't?

Vazquez smiles beneath his thin mustache. He talks about diet, about the prolonged cohabitation, about climate -- the perfect coming together of all these things that puts this pair, well, in the mood.

Apparently Mexico City's oppressive smog problem has had little effect on the pandas. The benefits of the 7,500-foot altitude, which is similar to that of their Chinese habitat, appears to offset whatever effects the miserably dirty air might have.

But the key point is the cohabitation. As Washington recently learned from its disastrous attempt to make a match between its female panda and that cad from London, these animals apparently don't kiss on the first date; they fight. Mexico's pandas were brought here before they were a year old. They have grown up together. Now "they play rough occasionally, but they never fight," said Vazquez.

The success of Pe-Pe and Ying-Ying ultimately remains a mystery, however, even to the zoologists who work with them every day. Nobody knows how these things will turn out.

"If a baby is born" -- Vanquez glanced upward -- "we'll say thank God, because God is a good guy with us."