Facing indignant demands from Egypt's antiquities chief, a corporate sponsor of a touring King Tut exhibition opening today in Chicago agreed yesterday to relinquish an ancient sarcophagus that is kept at its company headquarters.

Zahi Hawass, the hard-charging secretary general of Egypt's Supreme Council of Antiquities, learned of the artifact's existence on Wednesday at a preview for the press at the Field Museum. At the event, Randy Mehrbert, a representative of Exelon, the giant energy company based in Chicago, observed in his formal remarks that the company's chairman, John W. Rowe, had such a passion for Egyptian antiquities that he kept one in his office.

Dr. Hawass immediately demanded that organizers of the show drop Exelon as a sponsor unless it agreed to give the sarcophagus to the Field Museum or return it to Egypt. Late yesterday, after a flurry of meetings at the museum, a spokeswoman for Exelon announced the resolution.