Ajit Jain photo

Ajit Jain, a top lieutenant at Berkshire Hathaway, is on the short list of candidates to succeed Warren E. Buffett, Berkshire’s chief executive.

Mr. Jain has landed on another, less desirable list: He is a potential witness in the insider-trading trial of Rajat K. Gupta.

Mr. Gupta, a former director at Goldman Sachs and Procter & Gamble, faces federal criminal charges of illegally leaking information about those companies to the hedge fund manager Raj Rajaratnam, who was convicted last year of insider trading. Mr. Gupta is set to stand trial on April 9.

People briefed on the case say that the defense could use Mr. Jain, a friend of Mr. Gupta, as a character witness and have him testify that Mr. Gupta’s relationship with Mr. Rajaratnam was already frayed around the time prosecutors assert crimes occurred, giving him little incentive to share inside information.

Mr. Jain’s role in the case, which emerged in a pretrial conference Friday, adds to a list of prominent figures from Wall Street and corporate America who could testify in the trial in Federal District Court in Manhattan. Lloyd C. Blankfein, the chief executive of Goldman, and Gary D. Cohn, Goldman’s president, are possible witnesses. W. James McNerney Jr., a Procter & Gamble director and the chief executive of Boeing, could also be called to testify.

None of the potential witnesses are accused of wrongdoing. Goldman and Procter & Gamble spokesmen declined to comment. Berkshire representatives did not respond to requests for comment.

The case against Mr. Gupta, 63, has broadened the government’s sweeping insider trading crackdown beyond Wall Street trading floors and reached into some of the country’s most prestigious corporate boardrooms.

Prosecutors said last month that they would probably file additional criminal charges against Mr. Gupta. They have until Tuesday to file a new indictment.

The collection of big-name potential witnesses in the case speaks to the vast influence Mr. Gupta once held in the business world. As the global head of the management consulting giant McKinsey & Company, Mr. Gupta, a native of India, was a trusted adviser to corporate leaders like the private equity billionaire Henry R. Kravis. He counseled leading philanthropies, working with Bill Clinton and Bill Gates on their global health initiatives.