American Notes NEW YORK

Cheers rang out over the Beverly Hills junk-bond trading floor of Drexel Burnham Lambert at the news coming over the brokerage firm's wire. Jubilation also reigned among most New York Republicans, and quite probably in Mafia hangouts as well. Rudolph Giuliani, famed prosecutor of Wall Street manipulators (Drexel, Ivan Boesky), mobsters (the Colombo family) and corrupt politicians (former Bronx Democratic leader Stanley Friedman), announced that after 5 1/2 years as U.S. Attorney for the Southern District of New York, he would resign at month's end. Gotham Republicans, a tiny band of inveterate losers, delightedly anticipated being able this fall to field a candidate for mayor who might actually have a chance. Giuliani coyly remarked that "I have not shut the door on the possibility," and incumbent Edward I. Koch, who has been hurt by Giuliani's prosecutions of corrupt henchmen, allowed that the 44- year-old prosecutor would be a "very formidable candidate." Alternatively, the politically untested Giuliani might elect to follow in the footsteps of crime buster Thomas Dewey a half-century ago and run for Governor against Democrat Mario Cuomo next year.