Prices for the flat screens in televisions, personal computers and cellphones have plummeted in recent years  but the decline would have been even faster if it hadn’t been for an international price-fixing cartel, the Justice Department said on Wednesday.

Three leading flat-screen producers  LG Display of South Korea, Sharp of Japan and Chunghwa Picture Tubes of Taiwan  pleaded guilty and agreed to pay a total of $585 million in criminal fines for their role in fixing the price of liquid-crystal display panels.

LG is paying the most: a $400 million fine, the second-highest criminal fine ever imposed by the Justice Department’s antitrust division. The largest was the $500 million paid in 1999 by F. Hoffmann-La Roche, a Swiss pharmaceutical giant, for leading a price-fixing cartel in vitamin supplements.

The settlement, legal experts say, is unlikely to be the end of the flat-panel case. Under the settlement, the three companies have agreed to cooperate with the Justice Department’s continuing investigation. Thomas O. Barnett, assistant attorney general in charge of the department’s antitrust division, pointed out at a news conference on Wednesday that the American investigation involved the coordinated efforts of enforcement officials in Europe and Asia, as well as the United States.