Agile beam steering of optical radiation using phased arrays offers significant advantages, such as weight, stability, speed and power requirements, over conventional beam steering systems based on large optics, telescopes, and gimbals. Phased arrays incorporating programmable diffractive optics systems based on MEMS or liquid crystal spatial light modulators are being investigated for a number of applications including large aberration compensation, near-diffraction-limited imaging and agile beam steering. A prototype system uses discrete phase steps to approximate modulo-2π phase profiles and operates with 307,200 independently addressable elements, 100% fill factor and total optical efficiencies of up to 93%. This paper presents analysis of an agile beam steering phased array system incorporating physical parameters such as fill factor, 2π reset fidelity and influence function. Diffractive wavefront control with non-2π resets is shown to produce continual beam steering. Expressions and modeling of the far-field beam pattern and off-axis beam steering efficiency are presented. Measured diffraction efficiencies show close comparison with calculated values.