A power steering control valve can activate not only a power assist steering system but also a rear wheel steering system. The control valve includes valve elements relatively displaceable in response to a steering input torque to define therebetween parallel first and second fluid flow paths between an oil pump and a fluid reservoir to produce a first pressure difference in a front power cylinder in response to the steering torque. The valve elements define therebetween variable flow orifice means for producing a second pressure difference in a rear wheel power cylinder in response to the steering torque. The control valve also includes an externally controlled variable flow orifice valve. This orifice valve is arranged with respect to the variable flow orifice means such that it increases fluid flow passing therethrough in response to a second predetermined variable, such as a vehicle speed, to decrease the second pressure difference in the rear wheel power cylinder.