U.S. and Japanese officials are both expressing guarded pessimism early in the round of trade talks begun yesterday. The discussions aim to reduce the U.S.'s $60 billion trade deficit, due mostly to the sales of foreign-made autos here. The Clinton Administration is demanding that Tokyo increase the number of dealerships for American cars in Japan and that producers buy more American auto parts. Secretary of Commerce Ron Brown, in a televised interview, said an overall agreement is "probably unlikely." Trade Minister Ryutaro Hashimoto agreed, saying that there were "many hurdles yet to be overcome . . . on both sides." The meeting wasn't a total bummer. Japan looks likely to lower barriers for American medical supplies and telecommunications equipment.