John W. Sidgmore, 52, an executive whose company became the world's largest Internet access provider and who later presided over WorldCom Inc. as its bankruptcy case turned into the biggest in U.S. history, died Dec. 11 of complications of acute pancreatitis.

Mr. Sidgmore, of Potomac, had been hospitalized recently but had not been ill long, a family spokesman said.

Mr. Sidgmore, then vice chairman of WorldCom's board, became chief executive in April 2002 after founder Bernard J. Ebbers was forced to resign, but he held the position for only nine months. The following June, he disclosed that the company had improperly accounted for $3.9 billion in expenses, a figure that more than doubled later on.

A company investigative committee empaneled after WorldCom's bankruptcy said Mr. Sidgmore was the only board member who "seriously challenged management," though he, too, stopped questioning management after losing several battles with Ebbers. Ultimately, he failed to uncover the accounting practices that resulted in WorldCom's bankruptcy, the committee said.

Mr. Sidgmore rode the technology boom of the 1990s to its peak and then to its nadir. Like many, he was self-taught in technology: His degree from the State University of New York was in economics.

He was born in Suffern, N.Y. He started his career with General Electric Co. and rose to become general manager and vice president of GE Information Services, tripling the unit's net income on his way up the career ladder. From GE, Sidgmore went to a telecommunications software company in Bethesda, first called Telic Corp. and then Intelicom Solutions Corp. In 1991, Sidgmore helped negotiate the sale of the company to Computer Sciences Corp. of El Segundo, Calif.

One of Northern Virginia's "serial entrepreneurs," Mr. Sidgmore was president and chief executive of CSC Intelicom from 1989 to 1994. He went on to become president and chief operating officer of MFS Communications, which merged in 1995 with UUNet Technologies Inc., the world's largest Internet access provider, in a $2 billion deal. While Sidgmore was head of UUNet, its revenue grew from $6 million in 1995 to more than $4 billion in 1999.

In 1996, WorldCom bought UUNet. WorldCom bought MCI in 1998, and the company will take the MCI name after it emerges from bankruptcy.

Within weeks of becoming WorldCom CEO in 2002, Mr. Sidgmore revealed that the company had improperly accounted for expenses. The magnitude of the accounting scandal grew to $11 billion, and the company quickly sank into bankruptcy. He resigned as the firm was reorganized and new executives were brought in.

Mr. Sidgmore helped his former secretary Paula Jagemann launch eCommerce Industries Inc. while he was at WorldCom, and he remained chairman of the Vienna-based company, a provider of software to the office products industry. In September 2000, MicroStrategy Inc. chief executive Michael Saylor asked Sidgmore, already a member of MicroStrategy's board, to help turn around a troubled division called Strategy.com. It proved to be an insurmountable challenge, and the division was closed in September 2001.

Survivors include his wife, Randi, of Potomac; his son, Michael; his father, John Sr.; a brother; and a sister.

John W. Sidgmore took over WorldCom as it was beginning its descent into bankruptcy.