''This was not an intellectual exchange of ideas,'' he recalled. ''The banker was holding his chair. The guy who was head of mergers and acquisitions was running to get him some water. The word 'brilliant' was used seven or eight times.'' Some seven years later, Citigroup's shareholders may be ruing the day that the financial services conglomerate built by Mr. Weill set its sights on Mr. Ebbers and WorldCom. Last week, Citigroup agreed to pay $2.65 billion to settle a class-action lawsuit filed by investors who lost money in WorldCom, which filed for bankruptcy protection two years ago. It is the second-largest class-action settlement in history, after Cendant's, and the largest ever paid by a bank. Clearly, the bank's courtship of Mr. Ebbers, who was indicted last March on charges of securities fraud and conspiracy, is turning out to be costly.