They said federal prosecutors were aggressively pursuing the former chairman, and witnesses with information about him had recently testified before a special grand jury probing the December 2001 collapse.
Barring any delays, federal prosecutors aimed to seek an indictment before July 4, the sources said.
It is unclear what charges will be filed against Mr Lay, a friend and contributor to US President George W. Bush. But sources said any indictment would include conspiracy charges for helping to hide Enron’s true financial condition.
Former Enron CEO Jeffrey Skilling and top accountant Richard Causey are awaiting trial on charges of conspiracy, fraud and insider trading.
Mr Lay’s lawyer, Michael Ramsey, said he would ask to meet the Justice Department’s Enron task force this week.
“I feel very confident that Ken Lay did not commit a crime,” Mr Ramsey said.
Justice Department spokesman Bryan Sierra declined to comment.
The sources said prosecutors were probably focusing on Mr Lay’s actions and statements when he resumed as CEO upon Mr Skilling’s abrupt resignation in mid-August 2001.
Days after Mr Skilling’s resignation, Mr Lay privately met Sherron Watkins, then an executive on Enron finance chief Andrew Fastow’s staff, who had sent him a lengthy memo warning of impending doom from Mr Fastow’s schemes.