THE unexpectedly brief bond market rally in the United States surprised Hong Kong money and bond market dealers, who were left directionless in trading yesterday. US Treasury bonds enjoyed an Indian summer after the Federal Reserve raised both the funds rate and discount rate by 50 basis points on Tuesday. However, the rally was short-lived and the long-dated bonds suffered from heavy selling pressure on Thursday. Consequently, Hong Kong Government bonds closed about 20 basis points down in thin trading. ''The market no longer is so confident . . . that another interest rate is miles away from us,'' one market dealer said.