A method and apparatus are presented for transmitting acknowledgement (ACK)/negative acknowledgement (NACK) signals in a wireless communication system. ACK/NACKs are spread using spreading codes of a spreading factor, the spreading factor being one of a first spreading factor equal to 2 and a second spreading factor equal to 4. One or more physical hybrid automatic repeat request (ARQ) indicator channel (PHICH) groups allocated in units of four resource elements are transmitted, each PHICH group carrying up to four ACK/NACK signals for the first spreading factor, and up to eight ACK/NACK signals for the second spreading factor. A total number of allocated PHICH groups for the first spreading factor is determined as twice a total number of allocated PHICH groups for the second spreading factor. A PHICH group index for an ACK/NACK is determined using a first function. A spreading code index for the ACK/NACK is determined using a second function.