The explosion in College Park that killed a scholar from the People's Republic of China three weeks ago was caused by a bomb, Prince George County fire and police officials said yesterday.

Officials said they have not determined whether the bomb was directed at the scholar, Cuo Ren Wu, or the building where the bomb was lodged, the College Park municipal building.

Wu, 39, a visiting scholar at the University of Maryland, was across the street from the municipal building on June 27 when the bomb detonated at 12:18 a.m. The bomb was lodged on the outside of the building, on a concrete slab underneath an air conditioner on the ground, Fire Department Chief Jim Estepp said.

Immediately after the explosion, police and fire officials said it might have been caused by a malfunction in the air conditioner. But that possibility was ruled out after the U.S. Bureau of Standards and the Bureau of Alcohol, Tobacco and Firearms conducted laboratory analyses of pieces of matter collected from the scene of the explosion, Estepp said.

The homocide squad of the Prince George's County police department has begun an investigation to determine who planted the bomb and whether it was directed at Wu.

Wu was walking home from a party with four friends, also scholars from the People's Republic of China, when the bomb exploded. Wu's friends were treated for minor injuries at Prince George's General Hospital, but Wu died of his injuries on July 1.

"I'm not aware of what reasons may have been involved in setting off the bomb," Estepp said at a press conference. "Fact that they were from The People's Republic of China may or may not be relevant."

Officials refused to describe the bomb. It cause an estimated $100,000 worth of damage to the municipal center and shattered the windows of stores and cars within a 250-foot radius of the building, Estepp said.

The bomb was placed directly below the office of College Park Mayor St. Clair Reeves, but according to Donald Byrd, a town spokesman, there is "no reason to believe that it would be directed against the city government at all."

Wu's friends who were injured in the explosion said they found it difficult to believe that the bomb was aimed at them, or at Wu. "We didn't touch anybody in this society," said T. J. Fang. "We just go to the professors and came home."

Asked whether the bomb could have been aimed at them because they were from China, Z. H. Huang, who also was injured in the explosion, said: "I can't imagine how could someone know we five persons came from the People's Republic of China and not from Korea or Taiwan."

A State Department spokesman refused to rule out the possibility that the bomb was directed at Wu, saying, "To the best of our knowledge, no evidence so far has been turned up that would suggest the bombing was aimed at those Chinese students. But it's a matter that's still under investigation."

Wu was one of about 5,000 scholars from mainland China who study at universities throughout the world each year. About half of the scholars study in the United States, according to his friends, and about 50 of them are at Maryland.

A research scholar in the university's computer science department, Wu had been in the United States for three months. "He wanted to contribute toward the modernization of our country," said Huang.

The chairman of the computer science department, Raymond Yeh, said Wu had been doing background reading for his project on computer program restructuring methods.

Wu, who has a wife and two children in Peking, graduated in 1963 from the University of Nanking, where he majored in applied mathematics, according to his friends. He worked for a while in an institute for chemical engineers in China, his friends said, and then became a supervisor at the Kansu Computer Center in the province of Lanchow. He intended to return to the Kansu Computer Center in two years, his friends said.

Wu's friends who were with him when the bomb exploded say they have learned something from the experience about life in the United States. "It's very, very rare for such accidents to happen in China," said Huang. "But in America it's ordinary. It makes us frightened."