New York ? Citigroup Inc., the nation’s largest financial services company, on Friday said it would pay $2 billion to settle a class-action lawsuit over its role in helping Enron Corp. orchestrate a massive accounting fraud that led to the energy trader’s collapse.

The settlement marks the largest payout so far pledged to Enron investors, who claim they were bilked out of billions of dollars when the energy company went bankrupt in 2001. It also becomes one of the largest corporate settlements in history, but still below the $2.58 billion Citigroup agreed to pay WorldCom Inc. investors last year.

Some 50,000 stock and bondholders that filed claims as part of the lawsuit – led by the University of California’s board of regents – alleges some banks helped Enron defraud investors, continue operations and raise money even as the company was imploding. The settlement marks the fifth made in the long-running Enron debacle, and was seen as a catalyst for future deals with eight other banks targeted in similar lawsuits – including JPMorgan Chase & Co.

“We can’t predict the future, we don’t want to try and predict the future, but this development is obviously very favorable for our side of the case,” said William Lerach, the lawyer representing the lead plaintiff, the University of California, which lost millions when Enron declared bankruptcy.

In addition to JPMorgan Chase, class-action suits are pending against Barclays PLC, Credit Suisse First Boston, Merrill Lynch & Co., Toronto Dominion Bank, Royal Bank of Canada, Deutsche Bank AG and the Royal Bank of Scotland. Citigroup’s payment is more than four times the total of $491.5 million already received from settlements with Lehman Brothers Holdings Inc., Bank of America Corp., Andersen Worldwide, Enron’s outside directors and Ken Harrison, Enron’s former vice chairman.

As part of the settlement deal, Citigroup has denied committing any violation of law, saying it settled “solely to eliminate the uncertainties, burden and expense of further protracted litigation.”

Citigroup shares fell 4 cents to $47.64 in trading Friday on the New York Stock Exchange.