NEW YORK - Uncharacteristically on the defensive, billionaire Warren E. Buffett denied yesterday having been briefed on suspect transactions between a unit of his Berkshire Hathaway Inc. and insurance giant American International Group Inc.

Buffett, long known as an avatar of good corporate governance, is to be questioned April 11 by regulators in an investigation that focuses on "finite-risk insurance."

Berkshire said in a statement that Buffett, its chairman and chief executive officer, would appear voluntarily and that his submitting to questioning was part of the company's effort to cooperate with the investigation.

The regulators seemed eager to dispel the impression that the nation's best-known investor is suspected of wrongdoing.

"He is a witness, absolutely not a target," said a person at one of the investigating agencies who spoke on condition of anonymity.

The investigation, which began last fall, has knocked Maurice R. "Hank" Greenberg from his post as chief executive of AIG, which he had run since 1967 and turned into a global powerhouse.

Two weeks after resigning under pressure as CEO, Greenberg, 79, has agreed to step down as nonexecutive chairman. He is expected to leave the company today or tomorrow, after his return from a business trip to the Far East.

The investigation is being conducted by the Securities and Exchange Commission and the office of New York Attorney General Eliot Spitzer. The SEC subpoenaed Berkshire for documents Dec. 29, and Spitzer followed suit a week later.

The Buffett interview is expected to be conducted under oath, people familiar with the investigation said. Besides the SEC and New York attorney general's office, representatives of the U.S. Justice Department plan to participate, the sources said.

Among the questions that investigators are expected to ask Buffett, 74, is what he knew about transactions in late 2000 and early 2001 that Greenberg initiated between AIG and Berkshire's reinsurance subsidiary, General Re Corp.

Authorities think the transactions might have enabled AIG to boost its insurance premium revenue without taking on any risk beyond the amount of the premiums, which could violate accounting rules. An intentional effort to falsely inflate profit could be construed as fraud.

Berkshire took the unusual step yesterday of issuing a statement to rebut recent news stories about the investigation.

The Wall Street Journal, quoting an unidentified source, reported yesterday that investigators suspected Ron Ferguson, then chief executive of General Re, of briefing Buffett in 2000 "on the nature of the deal" with AIG.

"To the contrary," Berkshire said, "Mr. Buffett was not briefed on how the transactions were to be structured or on any improper use or purpose of the transactions."

Buffett's straightforward manner, sharp stock-picking skills and criticism of costly executive pay packages have made him a hero to many small and large investors. The current issue of Barron's ranks Buffett as one of the nation's 30 most-respected chief executives.

Berkshire, an Omaha, Neb., holding company whose insurance interests account for more than a quarter of its revenue, said it doesn't expect the investigation to result in any restatement of its financial reports.

General Re was subpoenaed two years ago in a separate investigation by the U.S. attorney for the Eastern District of Virginia. Regulators in Australia and Ireland also are scrutinizing the company.

Insurance carriers buy reinsurance to protect against potentially devastating claims resulting from natural disasters or sweeping legal judgments. Finite-risk insurance involves limited dollar amounts, as opposed to open-ended liability.

The Los Angeles Times is a Tribune Publishing newspaper.