The family of Richard Wertheim, the tennis umpire who died after striking his head on the ground when he was struck in the groin by a tennis ball during a match at last year's United States Open, sued the United States Tennis Association yesterday for $2.25 million.

The lawsuit, filed in state Supreme Court in Manhattan, accuses the association of negligence in providing adequate safety precautions for umpires, said Jacob Fuchsberg, whose law firm is handling the case.

The lawyer said Wertheim was officiating at the junior final when he was hit in the groin by a ball hit by Stefan Edberg of Sweden. ''He is a very prodigious player with a lot of speed,'' said Fuchsberg, who noted that tennis balls hit by professional athletes have been clocked at speeds higher than 100 mph.