Completion of a multichannel far-infrared ͑FIR͒ tangential interferometer/polarimeter is under way for the National Spherical Torus Experiment, for the measurement of plasma electron density and toroidal magnetic-field distributions. The system is based on the three-wavelength configuration, which was first developed by Rommers and Howard in the RTP tokamak ͓Plasma Phys. Controlled Fusion 38, 1805 ͑1996͔͒. The probe beams enter the plasma through the windows on the midplane in Bay-K, and are reflected back to the detectors by retro-reflectors. The three FIR beams with a wavelength of 119 m are produced by three Methanol lasers optically pumped by a CO 2 laser tuned to 9.7 m. The entire system is designed to have a full remote control capability using the LABVIEW program and fiber links. The technical details of the system development will be presented together with preliminary experimental result.