The introduction of magnetized plasma medium in the interaction region of a gyrotron-pumped free-electron laser (FEL) offers the possibility of generating short radiation wavelengths using moderate energy beams. The plasma slows down the electromagnetic wave produced by a high-power gyrotron that can now act as a wiggler for infrared free-electron laser. The wiggler period can be tuned by varying the plasma density and/or ambient magnetic field. The wiggler wave vector and its field amplitude are sensitive to the choice of wave frequency as this slow electromagnetic wave is dispersive in nature. The free-electron laser (FEL) operation for wiggler frequency close to electron cyclotron frequency is examined. The FEL efficiency and the gain are estimated.