City police, acting on a telephoned threat, said today they found a time bomb in a trash barrel just inside the main entrance at Boston Garden, hours before a Soviet team beat the NHL's Boston Bruins, 6-4, in a hockey exhibition.

The Boston Globe, quoting police sources, said the bomb was a live hand grenade wired to a timing device. But the sources said it was unclear whether the grendade was set to go off.

"Whoever did this meant business," a high-ranking police officer told the newspaper.

No arrests had been made, but the FBI and the U.S. Bureau of Alcohol, Tobacco and Firearms were called into the case.

The device was found 20 minutes after members of the Moscow Dynamo team arrived at the Garden. It was found by a Garden security guard and a police bomb squad officer, said a Garden security official who asked that he not be named.

"I just found out about it. I have no idea who did it. I condemn it," said Kenneth Sidman, head of the Boston chapter of the Jewish Defense League, as he arrived at the Garden for a planned demonstration. The 150 pickets carried signs and chanted "KGB go home." Two spectators were ejected, to cheers from the crowd of 11,458, for heckling the Dynamo team during the Soviet national anthem.

Sidman said he had asked the Bruins' management last month to cancel the match because, he said, the Dynamo squad is made up of Soviet police officers.