JACK-O-LANTERNS ON PARADE: Fire Chief Ben Zahn and Albert Coudron, chairman of the JCC-sponsored Halloween party at the Yost Field House at 7 o'clock tonight, display grotesque pumpkin-heads entered in the jack-o-lantern contest that will be a special feature of the entertainment for the city's youngsters. Chief Zahn is a judge in the contest. A variety of prizes have been donated by the JCC and local merchants for winners in the jack-o-lantern contest, a costume parade, and other events scheduled for the party. Opening feature of the Halloween celebration will be a parade, which will start at 6:45 in the 200 block of E. Huron St. and proceed to the Field House to the music of the Zal Gaz Grotto drum and bugle corps.