Techniques for sending and receiving acknowledgement (ACK) information in a wireless communication system are described. A base station sends control information and data to a user equipment (UE) and receives ACK information from the UE. The base station performs detection for the ACK information based on (i) a first hypothesis for the control information being missed by the UE and (ii) a second hypothesis for the control information being received correctly by the UE. In one design, the ACK information may have a variable size, and the base station may perform detection for the ACK information based on different block codes for the first and second hypotheses. In another design, the ACK information may have a fixed size, and the base station may perform detection for the ACK information based on a single block code and obtain a fixed number of bits for the ACK information for both hypotheses.