The problem of joint load management and admission control (JLAC) in underlay OFDMA-based cognitive radio networks (CRNs) is studied. The fraction of the active sub-carriers in a base station (BS) in each resource block (RB) is defined as the load factor of the BS per RB. In the JLAC problem, we simultaneously minimize the secondary users' outage ratio and the total load factors of the BSs via the RBs, subject to the constraint that the primary users are protected. This problem is a NP-hard problem. We first relax it into a convex optimization problem. Then, by employing the optimal solution to the relaxed JLAC problem, we derive a heuristic algorithm to gradually remove the most adversative secondary users imposing the most interference to the primary users. The performance of the proposed algorithm is studied in terms of the outage ratio of secondary users and the total load factors of the BSs via the RBs through extensive simulations.