The generation of quasisteady state plasmas in the power off phase, by short pulses [pulse duration (tau(p))similar to 0.5-1.2 mu s] of intense (60-100 kW) microwaves in the X band (9.45 GHz) is observed experimentally. The steady state is sustained from a few to tens of microseconds and depends upon the ionization processes in the interpulse phase and the characteristic diffusion length. The results are explained by a model, which considers the electron acceleration effects by the large amplitude of the field, the energy losses, and the characteristic electromagnetic field decay time. The effects of wave frequency, microwave power density, and particle diffusion on the steady state are investigated. A striking difference with conventional afterglows of pulsed discharges is pointed out. (c) 2007 American Institute of Physics.