The Leningrad University graduate had never met an American before. He said cautiously that he wanted to ask a few questions "which you don't have to answer if you don't want to"

"Go ahead," said the American, thinking wearily of those favorite topics of Soviet propaganda -- the neutron bomb, unemployment in the West, or perhaps the Camp David accords.

"My first question is about the flying saucer that followed the American astronauts to the moon and landed nearby. Why did the Americans suppress this, and can you really tell me about it?"

There was silence, and then the surprised American said that to his knowledge, there had been no such episode.

The Russian objected. He and his young friends, he went on, knew that Neil Armstrong and Buzz Aldrin had reported both a lunar landing by another craft, simultaneous with theirs in 1969, and a meeting and conversation with the extraterrestrial creatures. They had it on videotape, said the Russian.

When the American demurred, the young Soviet replied with disgust, "I see I know more about this than you!"

Soviet intelligentsia lacks zany fare such as "Close Encounters of the Third Kind," "Battlestar Galactica," or "Star Wars" to fire their imaginations. Nevertheless, the Soviet younger generation seems powerfully drawn to the romance of the saucers and other UFOs that reportedly have visited many capitalist countries in the past 30 years.

Study of the occult, of astrology, of zodiacal influences -- which the official Soviet press increasingly has scolded as "pseudo-science" -- seems to be on the increase here and, as elsewhere in the industrialized world, flying saucers are in the vanguard.

Interest in UFOs has been spurred by circulation of the text of a lecture, allegedly given and officially suppressed, by a man said to be a reliable scientist, Leon Zigel, who described the lunar meeting and added, "In the U.S.S.R. there exists a ban on all kinds of publications about UFOs."

That sentence alone is enough to ensure belief in clestial visitors, even though the samizdat (self-published) lecture has been denounced by various respected figures, including science fiction writer Yeremei Parnov.

Nevertheless this vast country, with its sparsely populated interior, has produced over the years other mysteries analagous to Western fixtures such as the Loch Ness Monster and "Big Foot," the legendary humanoid of the Pacific Northwest.

Last year, for example, on official Tass agency reporter suggested that the Abominable Snowman, or "yeti" of the Himalayas, may have a distant relation alive and well in northern Siberia. The Russian cousin is called "Chuchunaa" in a Yakutia dialect, which means "fugitive" or "outcast." The Tass reporter, Sergei Bulantsev, citing numerous reports from matter-of-fact natives of the Taiga, suggested Chuchunaa is a paleolithic humanold remnant who was driven into the wilderness by more agressive tribes.

According to the descriptions, Chuchunaa stands about six and a half feet high,is shaggy but wears a reindeer sking against the Siberian cold, eats meat and berries, has "a very dark face" the size of a human's but with a broad chin and a small forehead that protrudes above the eyes "like a cap."

Elsewhere, the search goes on for proof of the existence of an Aidakhor , a 50-foot Soviet version of the Loch Ness Monster. A Soviet geographer and his son reported seeing the monster one day in 1975, in a small lake called Kok-kol in the Dzhambul region of southern Kazakhstan. Soviet media, which excoriate the notion of the Loch Ness Monster as a circulation-building fabrication of the Sestern press, have paid some attention to their own creature from the depths. Unfortunately, the geographer was so frightened he forgot to take any photos.

As if there were not enough problems with these homegrown creatures, Soviet scientists have argued publicly over the mystery of the Bermuda Triangle, where the disappearance of many ships and planes over the years has been attributed to occult forces by some well-read Western authors.

All of these sightings and beliefs, fanciful or not, pale in comparison with the "Tunguska Enigma," one of the modern world's truly stupendous celestial events. On the night of June 30, 1908, a vast fireball from space streaked into the atmosphere over Siberia and exploded about four miles above the wilderness in a flash that was seen 750 miles away and whose concussion was recorded by barographs in London.

The marshland of the Tunguska River, where the thing exploded, was devastated: trees were shattered in an area of more than 800 square miles, wildlife was killed instantly, and villagers hundreds of miles away were knocked down by the concussion. Debris from the blast rose into the stratosphere and the dust altered sunsets in northern Europe for weeks after. Soviet scientists have estimated the blast at 40 million tons of high explosive, the power of a hydrogen bomb.

Soviet scientists and field researchers have studied the area of impact for more than 50 years. There is no crater; whatever the body was, it was vaporized without striking earth. In recent years, researchers have recovered from the tundra tiny spherical particles that are rich in sodium and silicon in combinations not found either on earth or in lunar soil samples. The Soviets think the firball was that of a stray comet that exploded from the effects of its own shock wave as it plunged toward earth at supersonic speed.