Decoherence effects on the traditional N vs. M photon coherent control of a two-level system are investigated, with I vs. 3 used as a specific example. The problem reduces to that of a two-level system interacting with a single mode field, but with an effective Rabi frequency that depends upon the fundamental and third harmonic fields. The resultant analytic control solution is explored for a variety of parameters, with emphasis on the dependence of control on the relative phase of the lasers. The generalization to off-resonant cases is noted. (c) 2005 Elsevier B.V. All rights reserved.