Techniques for supporting operation on multiple carriers are described. In an aspect, a carrier indicator (CI) field may be used to support cross-carrier assignment. The CI field may be included in a grant sent on one carrier and may be used to indicate another carrier on which resources are assigned. In one design, a cell may determine a first carrier on which to send a grant to a UE, determine a second carrier on which resources are assigned to the UE, set a CI field of the grant based on the second carrier and a CI mapping for the first carrier, and send the grant to the UE on the first carrier. The UE may receive the grant on the first carrier from the cell and may determine the second carrier on which resources are assigned to the UE based on the CI field of the grant and the CI mapping for the first carrier.