Summary form only given. A stable uniform, long-slit atmospheric argon plasma is produced by coupling a longitudinal section electric (LSE) mode in a dielectric loaded rectangular waveguide. The microwave-induced plasma discharge system consists of a 2.45 GHz microwave source, circulator, 3-stub tuner, transformer, and tapered rectangular waveguide loaded with two dielectric slabs. A uniform 98 mm long atmospheric argon plasma is observed at a relatively low microwave power level of 350 W and gas flow rate of I0-15 liters per minute