Manhattan's longtime district attorney, Robert M. Morgenthau, has decided not to seek reelection this year, several New York newspapers reported on their Web sites Friday.

Morgenthau, 89, has been a major force in New York's legal community for decades, serving as U.S. Attorney for the Southern District of New York and winning nine consecutive terms as Manhattan's district attorney.

"The challenge of his successor will be to fill the shoes of a giant," said Charles A. Stillman of Stillman, Friedman & Shechtman PC.

The New York Times and the New York Post, citing sources, reported Morgenthau has decided not to run again. The Post, citing sources, reported that Morgenthau has been privately telling top deputies in his office the news and is expected to make his intentions public in the next few weeks.

Morgenthau scheduled a press conference for 4:15 p.m. EST on Friday but didn't indicate the topic of the press conference.

A spokeswoman for Morgenthau's office didn't immediately have a comment Friday.

"If he does not run again, New York will be losing the best district attorney we ever had," said Stephen E. Kaufman, of Stephen E. Kaufman PC.

Morgenthau served in the U.S. Navy in World War II and began his legal career in 1948 after graduating from Yale Law School, joining Patterson, Belknap, Webb & Tyler LLP.

After 12 years of practicing corporate law, he was appointed U.S. Attorney for the Southern District of New York by President Kennedy in 1961 and created its much-touted securities-fraud unit.

"He's the father of white-collar prosecutions," said Gary P. Naftalis, of Kramer Levin Naftalis & Frankel LLP, who worked as an assistant U.S. attorney under Morgenthau. "Nobody really did it before him. He set the standard for all that."

Morgenthau resigned as U.S. Attorney in 1970 and won his first election as district attorney in 1974.

As district attorney, Morgenthau greatly increased the reach and breadth of the office, including pursuing international prosecutions and giving it white-collar focus it didn't previously have.

His office brought dozens of high-profile cases over the years, including ones involving rogue bank Bank of Credit & Commerce International, or BCCI; defunct brokerage firms A.R. Baron & Co. and Duke & Co.; and the former top executives of Tyco International Ltd (TYC).

In December 1991, liquidators for BCCI agreed to forfeit all of the bank's assets - $550 million - as part of a settlement with the U.S. Justice Department and Morgenthau's office. Sheik Kamal Adham, a major BCCI shareholder, in July 1992 pleaded guilty to a federal bank fraud charge and agreed to pay $105 million in fines.

A year later, Saudi Arabian financier Sheik Khalid bin Mahfouz agreed to pay $225 million to settle charges he conspired to steal more than $300 million from BCCI's depositors under an agreement with the Federal Reserve Board and Morgenthau's office.

In December 1997, A.R. Baron & Co., the defunct firm, pleaded guilty to a fraud that bilked investors out of $75 million, including manipulating initial public offerings and after-market trading in stocks. Twelve persons pleaded guilty and one was convicted at trial of criminal charges.

In the Duke & Co. case, the defunct firm's chairman, Victor Wang, and more than a dozen former employees pleaded guilty to criminal charges in a scheme to manipulate IPOs.

More recently, former Tyco top executives L. Dennis Kozlowski and Mark H. Swartz were convicted in 2005 on charges they systematically looted the company, which grew out of a sales-tax fraud inquiry by Morgenthau's office. Kaufman represented Kozlowski, and Stillman represented Swartz.

Last month, Lloyds TSB Group PLC's (LYG) banking unit entered into a deferred prosecution agreement with Morgenthau's office and federal authorities and forfeited $350 million in connection with an alleged scheme that allowed clients in Iran, Sudan and other countries to access the U.S. banking system, in violation of U.S. sanctions on those countries.

Morgenthau also influenced pop culture, serving as the model for the character of Adam Schiff, the original district attorney on NBC's long-running television series "Law & Order."

"[Morgenthau's] had a long history with the office, as well as U.S. attorney," said Mark C. Zauderer of Flemming Zulack Williamson Zauderer LLP. "There are some able and experienced people who are contending for the position."

Leslie Crocker Snyder, a former judge who has previously challenged Morgenthau, is one potential candidate for the office.

Cyrus Vance Jr., son of Jimmy Carter's secretary of state and a former prosecutor, and Richard Aborn, another former prosecutor, also have been raising money for a potential run.

Vance and Aborn both said Friday that they planned to enter the race for district attorney if Morgenthau doesn't seek another term.

Snyder didn't immediately return a call for comment.

-By Chad Bray, Dow Jones Newswires; 212-227-2017; chad.bray@dowjones.com