WorldCom and its former top executives have drawn intense scrutiny since last week, when the company disclosed it had discovered that $3.8 billion in operating expenses had been improperly accounted for, inflating the company's profits in 2001 and part of 2002. It fired Scott Sullivan as chief financial officer. Earlier this week, WorldCom also said it was investigating additional accounting problems, which people familiar with the matter said could add at least $1 billion to the company's accounting discrepancies. After allegedly being rebuffed by Mr. Sullivan, Ms. Cynthia Cooper took her findings to Max Bobbitt, chairman of the audit committee of WorldCom's board, who delayed taking action on her findings, according to a person close to the investigation. WorldCom has said that Mr. Bobbitt later turned over Ms. Cooper's findings to KPMG. Prosecutors have secured Ms. Cooper as a witness as they decide whether to bring criminal charges against WorldCom and some of its executives. The House Financial Services Committee, which is scheduled to hold hearings on WorldCom Monday, has been asked by the Justice Department to not call Ms. Cooper or Mr. Bobbitt to testify, according to a person with knowledge of the situation. Other executives are expected to testify, including WorldCom Chief Executive John Sidgmore.