Leslie R. Caldwell, a veteran prosecutor who directed the Justice Department's investigation of Enron Corp. until early this year, has joined the Morgan, Lewis & Bockius LLP law firm as a partner in its criminal defense and investigations unit.

The firm's top managers said Caldwell would take a lead role in expanding the business of representing white-collar defendants. "I'm tremendously excited to be joining a firm that has such a strong commitment to building a national white-collar practice," she said in an interview yesterday.

Morgan Lewis employs 1,200 lawyers in its offices around the world. It is perhaps best known for its labor and employment unit, which represents companies before the Labor Department and in private lawsuits.

Caldwell, 47, prosecuted gang members and organized crime families in her time as an assistant U.S. attorney in Brooklyn and San Francisco. But in recent years, she has attracted national attention for her role in rooting out widespread earnings manipulation at Enron, the Houston energy company that collapsed into bankruptcy in December 2001.

Federal prosecutors have charged 32 people in connection with Enron's demise, including former chief executives Kenneth L. Lay and Jeffrey K. Skilling. Both men are fighting the charges. Fourteen people with ties to Enron have pleaded guilty to various offenses.

Caldwell stepped down as head of the Enron Task Force shortly after the February indictment of Skilling. She will work out of Morgan Lewis's New York office.