We've heard a lot about the newly transformed, ready-to-reach-out Rudy Giuliani. Now he has a chance to prove it, by responding to a personal invitation from the Reverend Calvin Butts. This week's Harlem Renaissance Day breakfast has a lineup of sponsors you'd expect from the typical trendy Manhattan fund-raiser: Chase, American Express, Bell Atlantic, Citicorp, Bill Blass, Calvin Klein, and Oscar de la Renta (as well as this magazine). It might sound like the kind of worthy but not especially compelling event that usually brings wealthy people to the Plaza or the Waldorf to learn about the minority community. But the annual Renaissance breakfast, which raises money for the Abyssinian Development Corporation, demands a bit more of a commitment. Attendees actually have to go to 138th Street, and at 7:30 in the morning. It's a testament to both the work done by Abyssinian and the intense level of interest in Harlem that the event has grown in just five years from barely 100 people to more than 600. And while $100,000 was raised the first year, this week that figure will approach $550,000. The event has gotten so big that the only community locale able to accommodate it is the Great Hall at City College. But despite the importance of the breakfast as a community event, the smart money says 138th Street is still a little farther than the mayor is willing to travel.