The work provides an approach to default reasoningwith imperfect information using extended logic programsin multivalued logics given by bilattices. The paper introducesthe default semantics of an extended program usinga set of operators with interesting properties elegantly expressedin terms of lattice theory, including the ultimateevaluation based consequence operator and the default operatorcorresponding to two types of inference in presenceof imperfect information. We provide a computational approachfor the default semantics and relate our frameworkto relevant work.