Terrified, a boy began to scream, but with a stare of the alien's shining eyes, Tass said, the boy was silenced and paralyzed.

After a brief disappearance, the three returned, but this time one of the ''humanoids'' had ''what looked like a gun'' by his side - a tube about two feet long that it directed at a 16-year-old boy. The boy, whose name was not given in the report, promptly vanished, but reappeared after the alien embarked in the ball.

Vladimir A. Moiseyev, director of the regional health department, said in a telephone interview that despite reports of widespread fear in the city, none of the witnesses had applied for medical help. But he said that ''certainly we are planning to examine the children.'' There was no explanation why, with the passing of two weeks, such an examination had not yet taken place. Report Treated Seriously

Mr. Moiseyev, like other authorities in Voronezh, the editors of Tass, and indeed many of its readers, treated the report as a serious scientific phenomenon. No extra men are assigned to patrol the area because the department is short-handed, said the duty officer at the local Interior Ministry department, who identified himself only by his last name, Larin, but he said troops would be dispatched ''if they appear again.''

The Tass correspondent covering the case of the mysterious visitors to Voronezh, Vladimir V. Lebedev, seemed insulted that anyone would treat the story with anything but the full seriousness that it was given by the agency.

In a telephone interview, Mr. Lebedev described conversations with dozens of witnesses and with experts who had examined the evidence and spoken to the children. He said there were about three landings of the U.F.O between Sept. 23 and Sept. 29.

In the latest development, not yet reported by Tass, Mr. Lebedev said that Genrikh M. Silanov, head of the Voronezh Geophysical Laboratory, today asked the children to draw what they had seen. Drawings Said to Be Similar