House Banking Chairman Henry B. Gonzalez seems to be losing his lonely fight to block a Justice Dept. subpoena of records of the defunct House Bank. But his effort may be rewarded next December, when the erratic Texas Democrat is expected to face a challenge to his chairmanship. Although political fear caused them to vote to turn the records over, many members quietly cheered when Gonzalez and Representative Sidney R. Yates (D-Ill.) sought court action quashing the subpoena on separation-of-powers grounds. District and appeals courts have rejected the suit.