Experts have various theories about the recent rash of U.F.O. sightings. A recent article in the Journal of U.F.O. Research, published by the Gansu Science and Technology Press, notes that sightings in China peak each year around Oct. 1, China's National Day.

''If you think about it, it makes a lot of sense that visitors from an extraterrestrial civilization would come now,'' Mr. Jin said. ''We're entering a new millennium, so any extraterrestrial civilization that's been observing us would want to document the state of our civilization at this particular moment, as sort of a historical snapshot.''

He attributed the high frequency of sightings in China to its population density. And club officials say more than half of Chinese are interested in U.F.O.'s and believe that they might exist.

The Beijing U.F.O. Research Society has 280 members, and 30 percent are managers or Communist Party workers. The yearly research meetings of the national U.F.O. society are covered by reporters from the major news organizations.

This is an extraordinary reversal in a country where 25 years ago life was so focused on Communist politics that most people could not imagine anything so ethereal as an unidentified flying object, and expressing belief in them might have been a ticket to jail.

Indeed, Mr. Sun said he did not appreciate his one and only U.F.O. sighting -- a ''bright object in the sky'' -- in 1971, when he was sent to the countryside as a young Communist Party worker during the Cultural Revolution. ''I assumed it must be some sort of monitoring device, since relations between China and the Soviet Union were very tense at the time,'' he said, laughing. ''It was only years later, when I got more access to foreign materials, that I realized what I'd experienced.''

He and others credit China's two decades of liberalization and market reforms for allowing U.F.O. fever to flourish. ''As China has opened to the outside world in the last 20 years, people's thinking has also opened,'' he said.