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In this paper, a combined MLFMA-ACA approach is presented, which is applicable to three dimensional scattering problems of widely varying electrical sizes with complexity and fine structure. The classic MLFMA suffers breakdown at low frequencies, while ACA algorithm becomes less efficient than MLFMA at high frequencies. The presented algorithm combines these two methods to achieve stability at all frequencies. Also, it preserves the complexity of setup time, memory and matrix-vector multiplication time less than O(NlogN). Examples demonstrating CPU time and memory requirements are presented, and the efficient nature of the overall method is also demonstrated.