Perhaps the mystery surrounding the ancient kingdom of Kush in present-day Sudan will be resolved the day its language - written both in hieroglyphs and cursive letters - can be understood. For the moment, we can only marvel at the glimpses that its sculpture or its objects, many of them uncovered in recent excavations, allow us into a history as old as that of Egypt. "Sudan: Ancient Treasures," on view at the British Museum until Jan. 9, may be hopelessly pedestrian in its display, but if only for some of the stunning works on loan from the Sudan National Museum in Khartoum, this is one of the season's revelations.In the early phases, one looks in vain for a continuous thread. Information relating to objects is so scanty and vague as to be meaningless. Two remarkable earthenware vessels pieced together from fragments dug up at Jabarona in the Wadi Howar area, west of the Nile, are thus given dates some time between the fourth and second millennium B.C. We know nothing about the people who had that feeling for delicately burnished red surfaces and subtly translated into the potters' idiom patterns evidently derived from basketwork.Stupendously beautiful pottery was molded at Kerma. A small beaker with a burnished red lower part, irregular stripes of ashen gray half way up and a beautiful black sheen at the top ranks among the world masterpieces of ceramic art. A slightly earlier piece, a red and black shallow bowl, calls for comparison with early Dynastic pottery from Egypt for its color scheme but remains entirely original.