Maurice “Hank” Greenberg, ousted last month as chief executive officer of American International Group, will invoke his legal right to avoid self-incrimination when he testifies today before investigators probing the insurer’s accounting.

The former CEO will use his Fifth Amendment right not to answer questions from prosecutors examining a 4-year-old reinsurance transaction with Berkshire Hathaway’s General Re Corporation that AIG now says improperly distorted its finances. After meeting with investigators yesterday, Berkshire’s Warren Buffett said to reporters that he had “told them everything I know.”

Mr. Greenberg, 79, came to the decision not to testify after New York Attorney General Eliot Spitzer and the U.S. Securities and Exchange Commission refused his request to delay the deposition, said his attorney, David Boies, in a statement. There are thousands of documents linked to the investigation that Mr. Greenberg has not yet seen, Mr. Boies said.

“I am willing to accept responsibility and to account for the performance of my duties, but I believe that good order and fairness require that I have an adequate opportunity to be advised of the issues to be investigated and to my alleged involvement therein,” Mr. Greenberg said in a statement.

Mr.Buffett, 74, spent about five hours at the SEC’s offices in the Woolworth Building in downtown Manhattan today before emerging shortly after 2 p.m.

New York-based AIG said March 30 that improper accounting may have inflated its net worth by as much as $1.7 billion over 14 years. Mr. Spitzer told ABC News yesterday that he has “powerful evidence” and that he may be moving toward a civil or criminal case against Mr. Greenberg. AIG spokesman Chris Winans said the company continues to cooperate with investigators and declined to comment on Mr. Greenberg’s decision.

“Statements that seem innocuous and harmless at this juncture may later serve as lethal weapons,” said Christopher Bebel, a former federal prosecutor who now practices law in Houston.

Darren Dopp, Mr. Spitzer’s spokesman, didn’t return phone calls. Robert Morvillo, Mr. Greenberg’s criminal attorney, and SEC spokesman John Nester declined to comment.

Mr. Spitzer is focusing his AIG investigation on Mr. Greenberg, who stepped down as chairman and CEO last month after an almost four-decade reign. AIG “was a black box run with an iron fist by a CEO who did not tell the public the truth,” Mr. Spitzer told ABC.

Shares of AIG rose 19 cents to $52.10 in New York Stock Exchange composite trading.

Mr. Greenberg may have been tempted to ignore his safest option against the advice of his lawyers, said Rusty Hardin, a Houston attorney who represented Arthur Andersen LLP in its failed attempt to avoid obstruction of justice charges tied to Enron’s collapse.

The relevant accounting rules are debatable, and Mr. Greenberg would never have done the General Re transaction had he thought it was wrong, Mr. Boies said in an April 7 interview.

“For people like Greenberg who don’t believe they have done anything wrong, your first inclination is to tell everyone anything they might what to know,” Mr. Hardin said. “That isn’t always the wisest thing until you know what the other side is contending.”

Mr. Spitzer and the SEC last year began probing nontraditional, or finite, risk reinsurance, a type of reinsurance that became more popular in the 1990s and plays on the boundary between financing and insurance.

The accounting on finite risk can be abused if the insurer classifies what is essentially a low-cost loan from the reinsurer as reinsurance, thereby artificially reducing its liabilities. In the General Re transaction, AIG said on March 30 that it shouldn’t have been accounted for as reinsurance because there was no risk involved.

Investigators are also probing transactions with offshore reinsurers. Deals with Barbados-based reinsurer Union Excess Reinsurance alone may have inflated AIG’s net worth by $1.1 billion, the company said last month.

Mr. Boies said in the statement that Mr. Greenberg’s requests to delay the testimony to review documents were refused.