Donald I. Hovde said he withdrew his resignation from the Federal Home Loan Bank Board, which had been scheduled to take effect last Sunday, until a new member of the board is appointed by President Reagan. Had Hovde resigned, it would have left the three-member board, which regulates savings and loans, with just one member--its chairman, Edwin J. Gray. By law, the board cannot operate without a two-member quorum. Hovde said he had announced his resignation three months in advance in order to provide the Administration with adequate time to find a replacement. Bank board member Mary Grigsby resigned on Aug. 15. The Administration has given no indication of when it will announce nominations to fill the two spots.