If President Clinton thoughtWhitewater was a nightmare so far. . . just wait. Both future House and Senate committee chairs overseeing financial institutions are banking on going after the president once again -- this time with full subpoena-power and without pesky Dems curtailing their grilling of administration witnesses. Sen. Alfonse D'Amato (R-N.Y.), destined to chair the Banking Committee, says he'llresume hearingswithin 60 days of taking power in January. And he said he would not hesitate to use his subpoena power "if we find people not being cooperative." Rep. Jim Leach (R-Ia.), who will chair the House Banking Committee, issued a similar warning urging full White House cooperation.Post your opinion on theWashingtonbulletin board.