In this paper mode conversion of the ordinary wave to the extraordinary wave in a cold magnetized plasma at electron cyclotron frequencies is examined. A reduced set of wave equations, accounting for both the 2D inhomogeneity of the magnetic field and an arbitrary poloidal component of the magnetic field and coupling of the ordinary wave to the extraordinary wave near the O-mode cutoff surface, is derived. An integral representation of solutions to this set of equations is found. The conversion and reflection coefficients are calculated and analysed.