washing machine overflowing?

we have been having floods from our washing machine. It has become appearant it is overfilling and running over the top of the tub. It does not seem to be happening every time the machine is run but seems to be increasing in frequency. This leads me to believe it is some type of float switch which controls the water level that has gone bad, or perhaps gotten stuck or something. If this is the case where would such a device be located on the machine and how difficult would it be to obtain and install a replacement? This is a Roper brand medium sized machine with 2 load size selections, small & large, and has 4 cycles & 2 speeds.