ABSTRACT - Many creditors question whether J P Morgan Chase and Citigroup can represent their interests when, they contend, bank helped cause many of Enron's financial problems in first place; banks are subject of government investigations and private lawsuits over their role in structuring off-balance-sheet partnerships that helped sink Enron; some creditors say banks are in hopeless conflict, and Securities and Exchange Commission has expressed concern, as well; Wall Street firm Milbank, Tweed, Hadley & McCloy has been hired, at more than $1 million per month, to represent creditors committee in its negotiations with Enron; many creditors ask how effectively Milbank can represent them after having received more than $17 million in fees from Enron and its affiliates in last five years; Judge Arthur J Gonzalez, who is overseeing Enron bankruptcy, has scheduled hearing on May 15 on whether to disqualify Milbank; challenge to J P Morgan an d Citigroup is before Carolyn Schwartz, US trustee in case, who has power to remove members of creditors' committee and to refer matters for investigation or criminal prosecution; Harvard University Prof Elizabeth Warren says creditor representatives may risk suing themselves; chart; photos