3Com Corp. said it will fire 380 employees--150 of them temporary workers--at two Chicago-area plants and replace a top Illinois executive as the company struggles with product lines acquired in its 1997 purchase of U.S. Robotics Corp. Santa Clara-based 3Com, the No. 2 maker of networking equipment, said the employees worked at former U.S. Robotics plants that made desktop computer modems and remote-access servers used by businesses to route phone calls to the Internet. The fired workers represent about 7% of 3Com's Illinois work force. The company also said John McCartney, president of 3Com's client-access business unit, which includes modems and remote-access products, will leave the company next week. No replacement has been named. The news comes two weeks after 3Com said it was restating financial results related to the acquisition at the urging of the Securities and Exchange Commission. Shares of 3Com fell 50 cents to close at $33.50 on Nasdaq.