Harry Golden's back on the Lower East Side, a knish in one hand and a sour tomato in the other, revisiting the site of the old Yiddish Theater, the Educational Alliance, and P.S. 20 where Paul Muni, George Gershwin, Senator Jacob Javits, and Edward G. Robinson once attended classes in knee pants . . . Today of course most of the pushcart peddlers who sold everything from eyeglasses to grated horseradish are gone-victims of success American style, they're now merchandising high priced Paris couture in the Garment District, still dominated by Jewish entrepreneurs. The moral, mein kinder, is Moshe's aptitude for attainment whether it's Jan Peerce and the Metropolitan Opera, Isidor Straus and Macy's or Sandy Koufax and the Dodgers. That special Yiddishkeit culture has dispersed itself from Bensonhurst to the Bronx, touching every aspect of New York. Indulging in his usual genial ethnic thumpings (""The imagination and style of the city comes from Jewish chutzpa -- for which read imagination and guts""), Golden is as garrulous and complacent as ever about the Jewish achievement be it the dill in the chicken soup or the novels of Malamud or the interns at Albert Einstein Medical School. And secure enough to acknowledge that New York is also a great Irish city, a great Polish city, a great Italian city, a great Negro city, a great Puerto Rican city and, despite all the ethnic animosities, ""the most successful experiment in urban living ever conceived."" So dunk another bagel into the melting pot, bubala, and enjoy.