A new operator method is presented to derive from the two-fluid plasma model, the generalized Zakharov equations describing the coupled evolution of the high-frequency electric field and the low-frequency density and magnetic field perturbations. This method is particularly useful for the low-frequency equations, which are derived with no other assumptions than the neutrality condition, Del .Es=0, that is required to close the set of equations. In the steady-state case or when there is no external magnetic field, the low-frequency equations are identical to those found in the literature. In the general case, however, they differ by a few additional terms which account for finite wavelength effects.